Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Quantum molecule.
Дисертації з теми "Quantum molecule"
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "Quantum molecule".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Koch, Jens. "Quantum transport through single molecule devices." [S.l.] : [s.n.], 2006. http://www.diss.fu-berlin.de/2006/380/index.html.
Повний текст джерела
2
Hussain, A. "Time-dependent quantum dynamics of molecule predissociation." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604841.
Повний текст джерелаАнотація:
The work in this thesis uses wavepacket techniques on a discrete grid to solve the time-dependent Schroedinger equation numerically for a series of problems within the field of photodissociation dynamics. The systems studied focus on the phenomenon of 'predissociation', either electronically, via a non-adiabatic curve-crossing between (diabatically) bound and (diabatically) unbound Born-Oppenheimer potential energy surfaces (PESs), or vibrationally, in a system where there are several active vibrational modes, and the vibrational energy is enough to rupture one of the bonds provided enough can be concentrated in a single mode via intramolecular vibrational relaxation (IVR). The curve-crossing between the (bound) B and (repulsive) Y states of the I-Br molecule is studied in detail, being an example of electronic coupling that obeys neither the weak or strong limiting case. The dynamics of the B state are explored in detail, both via the propagation of coherent wavepackets, and by the propagation of the limiting (zero-coupling) vibrational eigenstates, to investigate the state-selectivity of the perturbation. It is found that the vibrational lifetimes vary dramatically with quantum number, with adjacent states often having half-lives that differ by two or three orders of magnitude. Finally, a series of calculations are performed simulating a set of pump-probe experiments that have been carried out on this system, and using the data previously generated on the B-state vibrational lifetimes to assist in the analysis. Qualitative agreement with experiment is achieved, and the data on vibrational lifetimes explains the main features of the ionisation traces; there is evidence that the model potentials (taken from the literature) are part of the explanation for any discrepancies.
3
Simmons, Christie. "The Quantum Dynamics of H2 in a C60 Lattice." Oberlin College Honors Theses / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1125601106.
Повний текст джерела
4
Ye, Lin Holder Andrew J. "Application of quantum mechanical QSAR to dental molecule design." Diss., UMK access, 2007.
Знайти повний текст джерелаАнотація:
Thesis (Ph. D.)--Dept. of Chemistry and School of Pharmacy. University of Missouri--Kansas City, 2007.<br>"A dissertation in chemistry and pharmaceutical science." Advisor: Andrew J. Holder. Typescript. Vita. Description based on contents viewed Apr. 15, 2008; title from "catalog record" of the print edition. Includes bibliographical references (leaves 89-93). Online version of the print edition.
5
Halstead, David Michael. "Time dependent quantum methods applied to molecule-surface interactions." Thesis, University of Liverpool, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303642.
Повний текст джерела
6
Krüger, Bastian Christopher. "From diatomic to polyatomic quantum-state-resolved molecule-surface scattering." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://hdl.handle.net/11858/00-1735-0000-0023-3F1E-7.
Повний текст джерела
7
Barry, John F. "Laser cooling and slowing of a diatomic molecule." Thesis, Yale University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3578337.
Повний текст джерелаАнотація:
<p> Laser cooling and trapping are central to modern atomic physics. It has been roughly three decades since laser cooling techniques produced ultracold atoms, leading to rapid advances in a vast array of fields and a number of Nobel prizes. Prior to the work presented in this thesis, laser cooling had not yet been extended to molecules because of their complex internal structure. However, this complexity makes molecules potentially useful for a wide range of applications. The first direct laser cooling of a molecule and further results we present here provide a new route to ultracold temperatures for molecules. In particular, these methods bridge the gap between ultracold temperatures and the approximately 1 kelvin temperatures attainable with directly cooled molecules (e.g. with cryogenic buffer gas cooling or decelerated supersonic beams). Using the carefully chosen molecule strontium monofluoride (SrF), decays to unwanted vibrational states are suppressed. Driving a transition with rotational quantum number <i>R</i>=1 to an excited state with <i> R'</i>=0 eliminates decays to unwanted rotational states. The dark ground-state Zeeman sublevels present in this specific scheme are remixed via a static magnetic field. Using three lasers for this scheme, a given molecule should undergo an average of approximately 100,000 photon absorption/emission cycles before being lost via unwanted decays. This number of cycles should be sufficient to load a magneto-optical trap (MOT) of molecules. In this thesis, we demonstrate transverse cooling of an SrF beam, in both Doppler and a Sisyphus-type cooling regimes. We also realize longitudinal slowing of an SrF beam. Finally, we detail current progress towards trapping SrF in a MOT. Ultimately, this technique should enable the production of large samples of molecules at ultracold temperatures for molecules chemically distinct from competing methods.</p>
8
Lane, Lucas A. "Advancement of blinking suppressed quantum dots for enhanced single molecule imaging." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54023.
Повний текст джерелаАнотація:
This work reports the development and spectroscopic studies of blinking-suppressed compact quantum dots. It is shown that a linearly graded alloy shell can be grown on a small CdSe core via a precisely controlled layer-by-layer process, and that this graded shell leads to a dramatic suppression of QD blinking both in organic solvents and in water. A substantial portion (over 25%) of the resulting QDs essentially does not blink (more than 99% of the time in the bright or “on” state). Theoretical modeling studies indicate that this type of linearly graded and relatively thin shells can not only minimize charge carrier access to surface traps, but also reduce accumulated lattice strains and defects at the core/shell interface, both of which are believed to be responsible for carrier trapping and QD blinking. Further, the biological utility of blinking-suppressed QDs by using both polyethylene glycol (PEG)-based and multidentate capping ligands is evaluated, and the results show that their optical properties are maintained regardless of surface coatings or solvating media, and that the blinking-suppressed QDs can provide continuous trajectories in live cell receptor tracking studies.
9
Wolter, Anja U. B. "Longitudinal and transverse magnetization in low-dimensional molecule-based quantum magnets." [S.l.] : [s.n.], 2006. http://www.digibib.tu-bs.de/?docid=00000066.
Повний текст джерела
10
Elste, Florian [Verfasser]. "Quantum transport through single-molecule devices: spin and vibration / Florian Elste." Berlin : Freie Universität Berlin, 2008. http://d-nb.info/1023023474/34.
Повний текст джерела
11
Rezai, Mohammad [Verfasser]. "Quantum Information Processing with Photons from a Single Molecule / Mohammad Rezai." München : Verlag Dr. Hut, 2018. http://d-nb.info/1172582009/34.
Повний текст джерела
12
Niederhausen, Thomas. "Quantum dynamics in laser--assisted collisions, laser--molecule interactions, and particle--surface scattering." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/313.
Повний текст джерела
13
Gonzalez, Jose Ignacio. "Quantum Optoelectronics: Nanoscale Transport in a New Light." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-04062006-110542/.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2006.<br>Dr. C. P. Wong, Committee Member ; Dr. C. David Sherrill, Committee Member ; Dr. Thomas M. Orlando, Committee Member ; Dr. Mostafa A. El-Sayed, Committee Member ; Dr. Robert M. Dickson, Committee Chair.
14
Caulfield, Jason M. "Magnetic quantum oscillations in organic metals based on the molecule bis(ethylenedithio)tetrathiafulvalene." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:5fbf2599-96d8-4eac-b882-ac74213ac3a5.
Повний текст джерелаАнотація:
ET charge transfer salts (where ET is <en>bis(ethylenedithio)- tetrathiafulvalene) have relatively simple quasi two-dimensional Fermi surface topologies, making them ideal for the study of the relationship between bandstructure and properties such as superconductivity. Experimental studies of the Fermi surface areas and associated effective masses have been carried out using the Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) effects. By comparing the experimental results to theoretical bandstructure calculations the strength of many body interactions has been estimated. High pressure magnetotransport experiments have been carried out on the superconductor κ-ET<sub>2</sub>Cu(NCS)<sub>2</sub>. The observation of SdH and magnetic breakdown oscillations has allowed the pressure dependences of the Fermi surface topology and effective masses to be deduced and compared with simultaneous measurements of the superconducting critical temperature. The data strongly suggest that the enhancement of the effective mass and the superconducting behaviour are directly connected. The results are compared with several current theories of superconductivity. The dHvA effect has been used to probe the superconducting mixed state of κ-ET<sub>2</sub>Cu(NCS)<sub>2</sub>. A recent model of the superconducting mixed state is applied to the experimental data in an attempt to determine the value and symmetry of the superconducting energy gap. SdH measurements up to 30 T have been used to study spin densitywave formation in α-ET<sub>2</sub>KHg(SCN)<sub>4</sub>, and the reasons why a very slight increase of the unit cell volume (i.e. replacing the K in α-ET<sub>2</sub>KHg(SCN)<sub>4</sub> by NH<sub>4</sub>) stabilises a superconducting state. Galvanomagnetic techniques have been used to measure the quasi onedimensional Fermi surface orientation below the spin-density-wave transition, and to accurately determine the shape of the quasi twodimensional Fermi surface above it. The application of pressure has been used to gradually reduce the onset temperature of a metal-insulator transition and to eventually stabilise a superconducting state in ET<sub>3</sub>Cl<sub>2</sub>2H<sub>2</sub>O. The bandstructure of ET<sub>3</sub>C1<sub>2</sub>2H<sub>2</sub>O has been investigated using the SdH effect whilst hydrostatic pressure has been used to pass through the superconducting part of the phase diagram.
15
Brown, Frank Leon Halet 1972. "Interactions of light with matter-- applications to single molecule spectroscopy and quantum control." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/47482.
Повний текст джерела
16
Cheng, Xiaolu. "Mixed Quantum/Semiclassical Theory for Small-Molecule Dynamics and Spectroscopy in Low-Temperature Solids." Thesis, University of Oregon, 2013. http://hdl.handle.net/1794/13001.
Повний текст джерелаАнотація:
A quantum/semiclassical theory for the internal nuclear dynamics of a small molecule and the induced small-amplitude coherent motion of a low-temperature host medium is developed, tested and applied to simulate and interpret ultrafast optical signals. Linear wave-packet interferometry and time-resolved coherent anti-Stokes Raman scattering signals for a model of molecular iodine in a 2D krypton lattice are calculated and used to study the vibrational decoherence and energy dissipation of iodine molecules in condensed media. The total wave function of the whole model is approximately obtained instead of a reduced system density matrix, and therefore the theory enables us to analyze the behavior and the role of the host matrix in quantum dynamics.
This dissertation includes previously published co-authored material.
17
Al-Khaykanee, Mohsin. "Quantum theory of electronic and thermal transport through nano-scale and single-molecule devices." Thesis, Lancaster University, 2018. http://eprints.lancs.ac.uk/90161/.
Повний текст джерелаАнотація:
This thesis presents a series of studies into the electronic, thermal and thermoelectric properties of molecular junctions containing single organic molecules. The exploration and understanding the electronic and phononic characteristics of molecules connected to metallic leads is a vital part of nanoscience if molecular electronics is to have a future. This thesis documents a study for various families of organic and organometallic molecules, studied using a combination of density functional theory (DFT), which is implemented in the SIESTA code, and the Green’s function formalism of transport theory. The main results of this thesis are as follows: To elucidate the nature of the high and low conductance groups observed in break-junction measurements of single 4,4-bipyridine molecules, I present a combined experimental and theoretical study of the electrical conductance of a family of 4,4-bipyridine molecules, with a series of sterically-induced twist angles α between the two pyridyl rings. I show that their conductances are proportional to cos2(α), confirming that pi-pi overlap between adjacent rings plays a dominant role. Since both peaks exhibit a cos2 (α) dependence of conductance on torsion angle, this is evidence that the high and low conductances correspond to molecular orientations within the junctions, in which the electrical current passes through the C-C bond linking the pi systems of the two rings. Furthermore, this result demonstrates that the Fermi energy is located within the HOMO-LUMO gap and not close to a transmission resonance. A theoretical investigation into the Seebeck coefficient in pi-stacked molecular junctions is performed using a first principles quantum transport method. Using oligo (phenyleneethynylene) (OPE)-type molecules as a model system, I show that quantum interference produces anti-resonances in the gap between the HOMO and LUMO resonances and the stacking geometry can control the position of this quantum interference feature. The shifting of this resonance enhances the thermopower S is expected when the junction is tuned through a node in the transmission function. We found supramolecular π-π interactions between two molecules changed the sign of thermopower. I have investigated a family molecules with various side branched atoms to study the electron and phonon transport through nanoscale molecular junctions, with a view to understanding the performance thermoelectric materials. My calculations focus on the effect of heteroatoms formed from C, Si, Ge, and Sn on the thermal phonon conductance, electrical conductance, and Seebeck Coefficient. I also examine how the thermoelectric figure of merit is affected by side branched atoms, as the bond length and mass play an important role in determining the thermal phonon conductance of molecular wires. Due to the rigid nature of C-side branching, the thermal phonon conductance decreases monotonically with the bond length and mass, whereas thermal phonon conductance with Si-side branches increases with the length of the bond and mass. The low thermal conductance kel with S-bridging, combined with their higher thermopower and higher electrical conductance leads to a maximum thermoelectric figure of merit of ZT = 1.76, which is several orders of magnitude higher than that of bridges.
18
Feng, Patrick Lulick. "Quantum magnetic phenomena in 0-D through 3-D MnIII₃-based single-molecule magnets." Diss., [La Jolla] : University of California, San Diego, 2010. http://wwwlib.umi.com/cr/ucsd/fullcit?p3389021.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--University of California, San Diego, 2010.<br>Title from first page of PDF file (viewed February 12, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
19
Sharkey, Keeper Layne. "Very Accurate Quantum Mechanical Non-Relativistic Spectra Calculations of Small Atoms & Molecules Employing All-Particle Explicitly Correlated Gaussian Basis Functions." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/560835.
Повний текст джерелаАнотація:
Due to the fast increasing capabilities of modern computers it is now feasible to calculate spectra of small atom and molecules with the greater level of accuracy than high-resolution measurements. The mathematical algorithms developed and implemented on high performance supercomputers for the quantum mechanical calculations are directly derived from the first principles of quantum mechanics. The codes developed are primarily used to verify, refine, and predict the energies associated within a given system and given angular momentum state of interest. The Hamiltonian operator used to determine the total energy in the approach presented is called the internal Hamiltonian and is obtained by rigorously separating out the center-of-mass motion (or the elimination of translational motion) from the laboratory-frame Hamiltonian. The methods utilized in the articles presented in this dissertation do not include relativistic corrections and quantum electrodynamic effects, nor do these articles assume the Born-Oppenheimer (BO) approximation with the exception of one publication. There is one major review article included herein which describes the major differences between the non-BO method and the BO approximation using explicitly correlated Gaussian (ECG) basis functions. The physical systems studied in this dissertation are the atomic elements with Z < 7 (although the discussion is not limited to these) and diatomic molecules such as H₂⁺ and H₂ including nuclear isotopic substitution studies with deuterium and tritium, as well as electronic substitutions with the muon particle. Preliminary testing for triatomic molecular functionals using a model potential is also included in this dissertation. It has been concluded that using all-particle ECGs with including the addition of nonzero angular momentum functions to describe nonzero angular momentum states is sufficient in determining the energies of these states for both the atomic and molecular case.
20
Ren, Hao. "First principles simulations of electron transport at the molecule-solid interface." Doctoral thesis, KTH, Teoretisk kemi (stängd 20110512), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12870.
Повний текст джерелаАнотація:
In this thesis I concentrate on the description of electron transport properties of microscopic objects, including molecular junctions and nano junctions, in particular, inelastic electron tunneling in surface-adsorbate systems are examined with more contemplations. Boosted by the rapid advance in experimental techniques at the microscopic scale, various electric experiments and measurements sprung up in the last decade. Electric devices, such as transistors, switches, wires, etc. are expected to be integrated into circuit and performing like traditional semiconductor integrated circuit (IC). On the other hand, detailed information about transport properties also provides new physical observable quantities to characterize the systems. For molecular electronics, which is in the state of growing up, its further applications demands more thorough understanding of the underlying mechanism, for instance, the effects of molecular configuration and conformation, inter- or intra-molecular interactions, molecular-substrate interactions, and so on. Inelastic electron tunneling spectroscopy (IETS), which reflects vibration features of the system, is also a finger print property, and can thus be employed to afford the responsibility of single molecular identification with the help of other experimental techniques and theoretical simulations.There are two parts of work presented in this thesis, the first one is devoted to the calculation of electron transport properties of molecular or nano junctions: we have designed a negative differential resistance (NDR) device based on graphene nanoribbons (GNRs), where the latter is a star material in scientific committee since its birth;The transport properties of DNA base-pair junctions are also examined by theoretical calculation, relevant experimental results on DNA sequencing have been explained and detailed issues are suggested.The second part focused on the simulation of scanning tunneling microscope mediated IETS (STM-IETS). We have implemented a numerical scheme to calculate the inelastic tunneling intensity based on Tersoff-Hamann approximation and finite difference method, benchmark results agree well with experimental and previous theoretical ones; Two applications of single molecular chemical identification are also presented following benchmarking.<br>QC20100630
21
Wen, Mary Mei. "New strategies for tagging quantum dots for dynamic cellular imaging." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52150.
Повний текст джерелаАнотація:
In recent years, semiconductor quantum dots (QDs) have arisen as a new class of fluorescent probes that possess unique optical and electronic properties well-suited for single-molecule imaging of dynamic live cell processes. Nonetheless, the large size of conventional QD-ligand constructs has precluded their widespread use in single-molecule studies, especially on cell interiors. A typical QD-ligand construct can range upwards of 35 nm in diameter, well exceeding the size threshold for cytosolic diffusion and posing steric hindrance to binding cell receptors. The objective of this research is to develop tagging strategies that allow QD-ligand conjugates to specifically bind their target proteins while maintaining a small overall construct size. To achieve this objective, we utilize the HaloTag protein (HTP) available from Promega Corporation, which reacts readily with a HaloTag ligand (HTL) to form a covalent bond. When HaloTag ligands are conjugated to size-minimized multidentate polymer coated QDs, compact QD-ligand constructs less than 15 nm in diameter can be produced. These quantum dot-HaloTag ligand (QD-HTL) conjugates can then be used to covalently bind and track cellular receptors genetically fused to the HaloTag protein. In this study, size-minimized quantum dot-HaloTag ligand conjugates are synthesized and evaluated for their ability to bind specifically to purified and cellular HTP. The effect of QD-HTL surface modifications on different types of specific and nonspecific cellular binding are systematically investigated. Finally, these QD-HTL conjugates are utilized for single-molecule imaging of dynamic live cell processes. Our results show that size-minimized QD-HTLs exhibit great promise as novel imaging probes for live cell imaging, allowing researchers to visualize cellular protein dynamics in remarkable detail.
22
Moreno, Pineda Eufemio. "New f-block and mixed d,f-block molecular nanomagnets." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/new-fblock-and-mixed-dfblock-molecular-nanomagnets(2f53085a-081b-4b27-a866-28f37f1fd633).html.
Повний текст джерелаАнотація:
Molecular Nanomagnets have been proposed as plausible candidates in a variety of futuristic applications. Thorough understanding of the magnetic properties of these systems is therefore necessary to develop devices that include such units. The aim of this thesis is to synthesise and structurally and magnetically characterise a range of systems that could be used as elementary units in three proposed applications such as: data storage devices, magnetic refrigerants and qubits for quantum computing. A series of mixed 3d/4f metal complexes were synthesised through solvothermal reactions and characterised by X-ray single crystal diffraction and SQUID magnetometry. Through indirect methods it was possible to obtain high magnetic entropy change for some systems. It was also possible to obtain some insight into the magnetic interactions within the systems through modelling the magnetic data. The role of the 4f-4f and 3d-4f interactions in two sets of molecules is also described. The first study is in an asymmetric dysprosium dimer, where through a range of experimental techniques and advanced theoretical methods, such ab-initio calculations we are able to explain the role of the intramolecular interactions and their effect on the SMM properties of this system. Similarly, insight into the role of the 3d-4f interactions is achieved through the observation of the magnetic behaviour of a family of 27 tetranuclear systems, though SQUID data and ab-initio calculations. Finally, chemical functionalization of a well-proposed qubits, namely {Cr7Ni} and subsequent reaction with a redox active metal ion, CoII/III, two {Cr7Ni} systems are linked. The magnitude of the exchange interaction between the {Cr7Ni}-CoII-{Cr7Ni} was determined through Electron Paramagnetic Resonance. Furthermore, by chemical oxidation/reduction of the cobalt between paramagnetic and diamagneticstates, i.e. CoII and CoIII respectively, we demonstrate that the interaction can be switched ON/OFF. This characteristic makes of these systems candidates to function as a SWAP gate.
23
Jenkins, Robert David. "Higher order energy transfer : quantum electrodynamical calculations and graphical representation." Thesis, University of East Anglia, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327601.
Повний текст джерела
24
Quddusi, Hajrah. "Role of internal degrees of freedom in the quantum tunneling of the magnetization in single-molecule magnets." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5442.
Повний текст джерелаАнотація:
The prominent features of single molecule magnets (SMMs), such as the quantum tunneling of the magnetization (QTM), are conventionally understood through the giant spin approximation (GSA) which considers the molecule as a single rigid spin. This model often requires the inclusion of high order anisotropy terms in the Hamiltonian, a manifestation of admixing of low lying excited states that can be more naturally understood by employing a multi-spin (MS) description i.e. considering the individual spins and the interactions between ions within the molecule. However, solving the MS Hamiltonian for high nuclearity molecules is not feasible due to the enormous dimensions of the associated Hilbert space that put it beyond the capability of existing computational resources. In contrast, low nuclearity systems permit the complete diagonalization of the MS Hamiltonian required to sample the effect of internal degrees of freedom, such as exchange interactions and single ion anisotropies, on the QTM. This dissertation focuses on the study of low nuclearity SMMs in view of understanding these subtle quantum effects. To accomplish this, we have developed a series of magnetic characterization techniques, such as integrated microchip sensors resulting from the combination of two dimensional electron gas (2DEG) Hall-Effect magnetometers and microstrip resonators, capable of performing measurements of magnetization and EPR spectroscopy simultaneously. The thesis bases on a comparative study of two low nuclearity SMMs with identical magnetic cores (Mn4 dicubane) but differing ligands. Notably, one of these SMMs lacked solvent molecules for crystallization; a characteristic that gives rise to extremely sharp resonances in the magnetization loops and whose basic QTM behavior can be well explained with the GSA. On the contrary, the second SMM exhibited mixed energy levels, making a MS description necessary to explain the observations. We have also examined the role of internal degrees of freedom on more subtle QTM phenomena, leading to the explanation of asymmetric Berry-phase interference patterns observed in a Mn4 SMM in terms of a competition between different intermolecular magnetic interactions, i.e. non-collinear zero-field splitting tensors and intramolecular dipolar interactions, resulting in astonishing manifestations of the structural molecular symmetry on the quantum dynamics of the molecular spin.<br>Ph.D.<br>Doctorate<br>Physics<br>Sciences<br>Physics
25
Sangtarash, Sara. "Theory of mid-gap quantum transport through single molecule : new approach to transport modeling of nanoelectronic devices." Thesis, Lancaster University, 2017. http://eprints.lancs.ac.uk/88312/.
Повний текст джерелаАнотація:
Molecules due to their very small sizes, possess discrete energy levels and electrons can transmit from one side of the molecule to the other with high probability if their energy coincides with molecular energy levels. In the weak coupling limit such on-resonance electron transport is described by the simple Lorentzian-shaped Breit-Wigner formula. On the other hand, electrons with energy different than the molecular energy levels have to tunnel through the energy gap between two molecular energy levels (off resonance transmission). Consequently the electron transmission probability is much smaller than on resonance regime. Interesting phenomena including quantum interference could be observed in this regime at room temperature. In this thesis, I discuss both regimes though, my main aim is to introduce a new theory called ”mid- gap theory” to predict the conductance ratio between different connectivities driven by quantum interference (QI) in the tunneling regime. Both theory and experiment have focused primarily on elucidating the conditions for the appearance of constructive or destructive interference. In the simplest case, where electrons are injected at the Fermi energy EF of the electrodes, constructive QI arises when EF coincides with a delocalized energy level En of the molecule. Similarly a simple form of destructive QI occurs when EF coincides with the energy Eb of a bound state located on a pendant moiety. Unless energy levels are tuned by electrostatic, electrochemical or mechanical gating, molecules located within a junction rarely exhibit these types of QI, because EF is usually located in the HOMO-LUMO (H-L) gap. Furthermore few analytic formulas are available, which means that pre-screening of molecules often requires expensive numerical simulations. For this reason, discussions have often focused on conditions for destructive or constructive QI when EF is located at the centre of the H-L gap. In this thesis, based on a simple description of connectivity, I demonstrate that the conductance ratio between two different connectivities of a core molecule could be predicted simply by using the ratio between two magic numbers of the core molecule. This will be discussed in the chapters 4-6. This simple theory not only predicts conductance ratios, but it could be used also to propose new strategies for molecular electronic design and applications such as single molecule switches and thermoelectricity. In this thesis after an introduction to nano and molecular electronics, I discuss general ideas about nanoscale transport and the methods which could be applied to model nano and molecular scale devices. In chapter 3, on resonance transport is discussed. For a wide variety of molecules, the conductance G decays with length L as Aexp(−βL) and it is widely accepted that the attenuation coefficient β is determined by position of the Fermi energy of the electrodes relative to the energy gap of the molecular bridge, whereas the terminal anchor groups which bind the molecule to the electrodes contribute to A. In contrast with this expectation, in chapter 3, I demonstrate that gateway orbitals located on the anchor groups can significantly decrease the value of β, thereby creating a new design strategy for realizing low-conductance molecular wires. In chapters 4-6, I introduce mid-gap theory and drive a mid-gap ratio rule (MRR) which is an exact formula for conductance ratios of tight-binding representations of molecules in the weak coupling limit, when the Fermi energy is located at the centre of the HOMO-LUMO (H-L) gap. It does not depend on the size of the H-L gap and is independent of asymmetries in the contacts. I also show how conductance ratios change, when one of the carbon atoms within the parent polycyclic aromatic hydrocarbons (PAH) core is replaced by a heteroatom to yield a daughter molecule. I show that this heteroatom substitution could be used to enhance the conductance in a PAH molecule by several orders of magnitude. A good agreement between this new simple theory and experiment shows that, the MRR provides a useful tool to predict the conductances of PAH molecules prior to synthesis. Therefore it could be used to design molecules with desirable properties or to propose new molecular devices.
26
Chapman, Craig Thomas 1980. "Vibrational wave packets: Molecular state reconstruction in the gas phase and mixed quantum/semiclassical descriptions of small-molecule dynamics in low-temperature solid media." Thesis, University of Oregon, 2010. http://hdl.handle.net/1794/10584.
Повний текст джерелаАнотація:
xiv, 195 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.<br>We explore the reconstruction of B-state vibrational wave packets in I 2 from simulated two-color nonlinear wave packet interferometry data. As a simplification of earlier proposals, we make use of different vibrational energy ranges in the B-state--rather than different electronic potential surfaces--for the short-pulse preparation and propagation of both target and reference wave packets. Numerical results from noisy interferograms indicate that experimental reconstruction should be possible with high fidelity (>0.99). Time-resolved coherent nonlinear optical experiments on small molecules in low-temperature host crystals are exposing valuable information on quantum mechanical dynamics in condensed media. We make use of generic features of these systems to frame two simple, comprehensive theories that will enable the efficient calculation of their ultrafast spectroscopic signals and support their interpretation in terms of the underlying chemical dynamics. Both treatments rely on the identification of normal coordinates to unambiguously partition the well-structured guest-host complex into a system and a bath and expand the overall wave function as a sum of product states between fully anharmonic vibrational basis states for the system and approximate Gaussian wave packets for the bath degrees of freedom. The theories exploit the fact that ultrafast experiments typically drive large-amplitude motion in a few intramolecular degrees of freedom of higher frequency than the crystal phonons, while these intramolecular vibrations indirectly induce smaller-amplitude--but still perhaps coherent--motion among the lattice modes. The equations of motion for the time-dependent parameters of the bath wave packets are fairly compact in a fixed vibrational basis/Gaussian bath (FVB/GB) approach. An alternative adiabatic vibrational basis/Gaussian bath (AVB/GB) treatment leads to more complicated equations of motion involving adiabatic and nonadiabatic vector potentials. Numerical tests of the FVB/GB are presented. We consider two bilinearly coupled harmonic oscillators with varying coupling strengths and initial conditions and show that the mixed quantum/semiclassical theory compares favorably with the exact results. Linear absorption spectra and wave-packet interferometry signals calculated using the theory are presented. This dissertation includes previously published coauthored material.<br>Committee in charge: David Herrick, Chairperson, Chemistry;
Jeffrey Cina, Advisor, Chemistry;
Thomas Dyke, Member, Chemistry
Michael Kellman, Member, Chemistry;
Hailin Wang, Outside Member, Physics
27
Kay, Mark. "A study of quantum and classical dynamical simulations of the Hâ†2 molecule incident on the W(100) surface." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243104.
Повний текст джерела
28
Thiele, Stefan. "Read-out and coherent manipulation of an isolated nuclear spin using a single-molecule magnet spin-transistor." Phd thesis, Université de Grenoble, 2014. http://tel.archives-ouvertes.fr/tel-00984973.
Повний текст джерелаАнотація:
La réalisation d'un ordinateur quantique fonctionnel est l'un des objectifs tech- nologiques les plus ambitieux pour les scientifiques d'aujourd'hui. Sa brique de base est composée d'un système quantique à deux niveaux, appelé bit quantique (ou qubit). Parmi les différents concepts existants, les dispositifs à base de spin sont très attractifs car ils bénéficient de la progression constante des techniques de nanofabrication et permettent la lecture électrique de l'état du qubit. Dans ce contexte, les dispositifs à base de spins nucléaires offrent un temps de cohérence supérieur à celui des dispositifs à base de spin electronique en raison de leur meilleure isolation à l'environnement. Mais ce couplage faible a un prix: la détection et la manipulation des spins nucléaires individuels restent des tâches difficiles. De très bonnes conditions expérimentales étaient donc essentielles pour la réussite de ce projet. Outre des systèmes de filtrage des radiofréquences à très basses températures et des amplificateurs à très faible bruit, j'ai développé de nouveaux supports d'échantillons et des bobines de champ magnétique trois axes compacts avec l'appui des services techniques de l'Institut Néel. Chaque partie a été optimisée afin d'améliorer la qualité de l'installation et évaluée de manière quantitative. Le dispositif lui-même, un qubit réalisé grâce à un transistor de spin nucléaire, est composé d'un aimant à molécule unique couplé à des électrodes source, drain et grille. Il nous a permis de réaliser la lecture électrique de l'état d'un spin nucléaire unique, par un processus de mesure non destructif de son état quantique. Par conséquent, en sondant les états quantique de spin plus rapidement que le temps de relaxation caractéristique de celui-ci, nous avons réalisé la mesure de la trajectoire quantique d'un qubit nucléaire isolé. Cette expérience a mis en lumière le temps de relaxation T1 du spin nucléaire ainsi que son mécanisme de relaxation dominant. La manipulation cohérente du spin nucléaire a été réalisée en utilisant des champs électriques externes au lieu d'un champ magnétique. Cette idée originale a plusieurs avantages. Outre une réduction considérable du chauffage par effet Joule, les champs électriques permettent de contrôler et de manipuler le spin unique de façon très rapide. Cependant, pour coupler le spin à un champ électrique, un processus intermédiaire est nécessaire. Un tel procédé est l'interaction hyperfine, qui, si elle est modifiée par un champ électrique, est également désigné sous le nom d'effet Stark hyperfin. En utilisant cet effet, nous avons mis en évidence la manipulation cohérente d'un spin nucléaire unique et déterminé le temps de cohérence T2 . En outre, l'exploitation de l'effet Stark hyperfin statique nous avons permis de régler le qubit de spin nucléaire à et hors résonance par l'intermédiaire de la tension de grille. Cela pourrait être utilisé pour établir le contrôle de l'intrication entre les différents qubits nucléaires. En résumé, nous avons démontré pour la première fois la possibilité de réaliser et de manipuler un bit quantique basé sur un aimant à molécule unique, étendant ainsi le potentiel de la spintronique moléculaire au delà du stockage de données classique. De plus, la grande polyvalence des molécules aimants est très prometteuse pour une variété d'applications futures qui, peut-être un jour, parviendront à la réalisation d'un ordinateur quantique moléculaire.
29
Flores, Gonzalez Jessica. "Isotopic Enrichments of lanthanide based single molecule magnets." Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1S064.
Повний текст джерелаАнотація:
Les matériaux moléculaires, et plus précisément ceux à base d’ions lanthanides, ont été largement étudiés pour leur utilisation dans différentes applications, dont le stockage de l’information ou l’ordinateur quantique. Cet intérêt s’explique du fait que des systèmes contenant des ions lanthanides donnent lieu à une large anisotropie et une bistabilité magnétiques d‘origine purement moléculaire. Durant les vingt-cinq dernières années, beaucoup d’articles ont été publiés dans lesquels les composés à base de ces ions montraient une relaxation lente de leur aimantation et une hystérèse magnétique à basse température. Récemment, des recherches ont menées à l’obtention de systèmes moléculaires présentant des températures de blocage (température maximale à laquelle le système se comporte comme à superparamagnétique) proche de l’azote liquide ce qui facilite le transfert dans des dispositifs basés sur ces systèmes.Cependant, cette relaxation lente de l’aimantation est souvent accompagnée des phénomènes quantiques, donnant lieu à d’autres relaxations beaucoup plus rapides. Les phénomènes quantiques peuvent donner lieu à de nouvelles applications mais à condition de bien comprendre leurs mécanismes d’action. Les interactions dipolaires et les hyperfines, les premiers provenant des molécules voisines et la deuxième de l’interaction spin-noyau dans le métal, sont connus pour participer à l’origine de ces phénomènes. Quelques systèmes ont été choisis durant ce travail de thèse dans le but de mieux comprendre les évènements quantiques et la contribution des différentes interactions. Ceci a mené à la synthèse et aux caractérisations magnétiques de différents systèmes magnétiquement dilués (étude des interactions dipolaires) et isotopiquement enrichis (étude des interactions hyperfines), afin de mettre en évidence une tendance générale pour l’optimisation des processus de relaxation lente<br>Molecular materials, and in particular those based on Lanthanides, have been extensively studied for their use in data storage, spintronics and quantum computing, as they promise high anisotropic systems and magnetic bistability of the discrete entity. Actually, in Athe last twenty-five years a plethora of compounds have been reported, thus showing slow of their magnetic relaxation and the characteristic magnetic hysteresis at low temperature. Moreover, some of the last investigations have reach blocking temperatures (temperature for which the system shows superparamagnetic behavior) at the liquid nitrogen level, hence facilitating the applicability of devices based on these molecules. However, the slow relaxation is commonly accompanied by quantum phenomena, favoring a fasten relaxation. The quantum effects open the possibility to different magnetic objects, but only if the operating mechanisms are well known. Dipolar interactions, with the neighboring molecules, and hyperfine interactions, with the metal ion, are known to be some of the reasons why this fast relaxations occurs. With the aim of acquiring a better understanding of the quantum events, and the contribution of the different interactions, different systems have been chosen to be studied in this work. Thus, the synthesis and magnetic characterization of magnetically diluted (suppression of dipolar interactions) and isotopic enrichment (tuning of the hyperfine interactions) of the different systems have been performed in order to find a general direction for the optimization of the slow relaxation process
30
Batchelor, Colin. "Molecular Rydberg dynamics." Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:46b5699b-1dcf-4860-8d76-09fc487a09d4.
Повний текст джерелаАнотація:
A simple theory relating the dynamics of electrons to the long-range properties of the molecular ionic core is developed for asymmetric top molecules in general and water in particular. It is combined with the molecular version of multichannel quantum defect theory developed by Fano and Jungen and applied to the resonance-enhanced multiphoton ionization spectra of Child and Glab (M. S. Child and W. G. Glab, J. Chem. Phys., 2001, 112, 3754-3765), the mass-analysed threshold ionization spectra of Dickinson et al. (H. Dickinson, S. R. Mackenzie and T. P. Softley, Phys. Chem. Chem. Phys., 2000, 2, 4669-4675) and the as-yet unpublished work of Glab on the photoelectron branching ratios of the nd and nf Rydberg lines of the water molecule. The effect of resonances between electronic and rotational motion in Rydberg molecules is investigated using multichannel quantum defect theory with special reference to the time-resolved wave packet experiments of Smith et al. (R. A. L. Smith, J. R. R. Verlet, E. D. Boleat, V. G. Stavros and H. H. Fielding, Faraday Discuss., 2000, 115, 63-70).
31
Waltersson, Erik. "On the role of the electron-electron interaction in two-dimensional quantum dots and rings." Doctoral thesis, Stockholms universitet, Fysikum, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-38862.
Повний текст джерелаАнотація:
Many-Body Perturbation Theory is put to test as a method for reliable calculations of the electron-electron interaction in two-dimensional quantum dots. We show that second order correlation gives qualitative agreement with experiments on a level which was not found within the Hartree-Fock description. For weaker confinements, the second order correction is shown to be insufficient and higher order contributions must be taken into account. We demonstrate that all order Many-Body Perturbation Theory in the form of the Coupled Cluster Singles and Doubles method yields very reliable results for confinements close to those estimated from experimental data. The possibility to use very large basis sets is shown to be a major advantage compared to Full Configuration Interaction approaches, especially for more than five confined electrons. Also, the possibility to utilize two-electron correlation in combination with tailor made potentials to achieve useful properties is explored. In the case of a two-dimensional quantum dot molecule we vary the interdot distance, and in the case of a two-dimensional quantum ring we vary the ring radius, in order to alter the spectra. In the latter case we demonstrate that correlation in combination with electromagnetic pulses can be used for the realization of quantum logical gates.<br>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Manuscript.
32
Bull, James. "Application of Quantum Mechanics to Fundamental Interactions in Chemical Physics: Studies of Atom-Molecule and Ion-Molecule Interactions Under Single-Collision Conditions: Crossed Molecular Beams; Single-Crystal Mössbauer Spectroscopy: Microscopic Tensor Properties of ⁵⁷Fe Sites in Inorganic Ferrous High-Spin Compounds." Thesis, University of Canterbury. Department of Chemistry, 2010. http://hdl.handle.net/10092/4292.
Повний текст джерелаАнотація:
As part of this project and in preparation for future experimental studies of gas-phase ion-molecule reactions, extensive modification and characterization of the crossed molecular beam machine in the Department of Chemistry, University of Canterbury has been carried out. This instrument has been configured and some
preliminary testing completed to enable the future study of gas-phase ion-molecule collisions of H⁺₃ and Y⁻ (Y
= F, Cl, Br) with dipole-oriented CZ₃X (Z = H, F and X = F, Cl, Br). Theoretical calculations (ab initio
and density functional theory) are reported on previously experimentally characterized Na + CH₃NO₂, Na + CH₃NC, and K + CH₃NC systems, and several other systems of relevance. All gas-phase experimental and theoretical studies have the common theme of studying collision orientation dependence of reaction under singlecollision
conditions. Experimental measurements, theoretical simulations and calculations are also reported on some selected ferrous (Fe²⁺) high-spin (S=2) crystals, in an attempt to resolve microscopic contributions of two fundamental macroscopic tensor properties: the electric-field gradient (efg); and the mean square displacement (msd) in the case when more than one symmetry related site of low local point-group symmetry contributes to the same quadrupole doublet. These determinations have been made using the nuclear spectroscopic technique of Mössbauer spectroscopy, and complemented with X-ray crystallographic measurements.
33
Sperl, Alexander Georg [Verfasser], and Joachim [Akademischer Betreuer] Ullrich. "XUV-IR pump-probe experiments: Exploring nuclear and electronic correlated quantum dynamics in the hydrogen molecule / Alexander Georg Sperl ; Betreuer: Joachim Ullrich." Heidelberg : Universitätsbibliothek Heidelberg, 2013. http://d-nb.info/1177148536/34.
Повний текст джерела
34
Camarasa, Gomez Maria [Verfasser], Ferdinand [Akademischer Betreuer] Evers, and Jaroslav [Akademischer Betreuer] Fabian. "Ab Initio Electronic Transport in Single-Molecule Junctions: Quantum Interference Effects and Spin-Orbit Torque / Maria Camarasa Gomez ; Ferdinand Evers, Jaroslav Fabian." Regensburg : Universitätsbibliothek Regensburg, 2021. http://d-nb.info/1240901798/34.
Повний текст джерела
35
Schinabeck, Christian [Verfasser], Michael [Akademischer Betreuer] Thoss, Michael [Gutachter] Thoss, and Florian [Gutachter] Marquardt. "Hierarchical quantum master equation approaches to nonequilibrium charge transport through single-molecule junctions / Christian Schinabeck ; Gutachter: Michael Thoss, Florian Marquardt ; Betreuer: Michael Thoss." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2019. http://d-nb.info/1186380705/34.
Повний текст джерела
36
Barhoumi, Rabei. "Positioning and addressing single molecule magnets with an STM tip." Thesis, Strasbourg, 2019. https://publication-theses.unistra.fr/restreint/theses_doctorat/2019/BARHOUMI_Rabei_2019_ED182.pdf.
Повний текст джерелаАнотація:
Les aimants moléculaires de type TbPc2 avec leur anisotropie magnétique élevée associée à des temps de relaxation longs de l’aimantation sont de bons candidats pour le codage et l’enregistrement de l’information. Leur robustesse et leur propension à s’arranger en réseaux se prêtent bien à une étude de leur structure électronique et magnétique par STM/STS à très basse température (4.5 K). Dans ce travail de thèse, il a été possible de mettre en évidence un écrantage Kondo des électrons π et 4f de la molécule de TbPc2 par les électrons du substrat métallique. Les propriétés magnétiques de la molécule dépendent de leur degré d’interaction avec le substrat et des interactions latérales avec les autres molécules. Ainsi le radical π de la molécule est préservé sur Au(111) mais disparait sur Ag(111) sous l’effet d’un transfert de charge entre le substrat et la monocouche moléculaire. Enfin, lorsque la molécule est en interaction forte avec le substrat de Cu(111), un accès direct aux états 4f de l’ion central de Tb est observé par STM comme le montre la détection d’un effet Kondo sur l’ion central de Tb<br>With their large magnetic anisotropy associated with long relaxation times of the magnetization, TbPc2 molecular magnets are good candidates for encoding and recording data. Their robustness and their propensity to arrange into networks lend themselves well to a study of their electronic and magnetic structure by STM/STS at very low temperature (4.5 K). In this thesis work, it was possible to highlight a Kondo screening of the π and 4f electrons of the TbPc2 molecule by the electrons of the metal substrate. The magnetic properties of the molecule depend on their degree of interaction with the substrate and lateral interactions with other molecules. Thus, the π radical of the molecule is preserved on Au (111) but disappears on Ag (111) under the effect of a charge transfer between the substrate and the molecular monolayer. Finally, when the molecule is in strong interaction with the Cu(111) substrate, a direct access to the 4f states of the central Tb ion by STM is possible as shown by the detection of a Kondo effect on the central Tb ion
37
Chang, Yuan-Pin. "Novel probes of angular momentum polarization." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:d3880edf-436a-415e-8a74-6b1c0fd26e65.
Повний текст джерелаАнотація:
New dynamical applications of quantum beat spectroscopy (QBS) to molecular dynamics are employed to probe the angular momentum polarization effects in photodissociation and molecular collisions. The magnitude and the dynamical behaviour of angular momentum alignment and orientation, two types of polarization, can be measured via QBS technique on a shot-by-shot basis. The first part of this thesis describes the experimental studies of collisional angular momentum depolarization for the electronically excited state radicals in the presence of the collider partners. Depolarization accompanies both inelastic collisions, giving rise to rotational energy transfer (RET), and elastic collisions. Experimental results also have a fairly good agreement with the results of quasi-classical trajectory scattering calculations. Chapter 1 provides the brief theories about the application of the QBS technique and collisional depolarization. Chapter 2 describes the method and instrumentation employed in the experiments of this work. In Chapter 3, the QBS technique is used to measure the total elastic plus elastic depolarization rate constants under thermal conditions for NO(A,v=0) in the presence of He, Ar, N2, and O2. In the case of NO(A) with Ar, and particularly with He, collisional depolarization is significantly smaller than RET, reflecting the weak long-range forces in these systems. In the case of NO(A)+N2/O2, collisional depolarization and RET are comparable, reflecting the relatively strong long-range forces in these systems. In Chapter 4, the QBS technique is used to measure the elastic and inelastic depolarization and total RET rate constants for OH(A,v=0) under thermal conditions in the presence of He and Ar, as well as the total depolarization rate constants under superthermal conditions. In the case of OH(A)+He, elastic depolarization is sensitive to the N rotational state, and inelastic depolarization is strongly dependent on the collision energy. In the case of OH(A)+Ar, elastic depolarization is insensitive to N, and inelastic depolarization is less sensitive to the collision energy, reflecting that the relatively strong long-range force in OH(A)+Ar system. The second part of this thesis describes the experimental studies of photodissociation under thermal conditions. Chapter 5 provides a brief introduction about several polarization parameter formalisms used for photodissociation, and the incorporation of the QBS technique to measure these polarization parameters. In this thesis, most polarization parameters of the molecular photofragments are measured using the LIF method, and the QBS technique is used as a complementary tool to probe these polarization parameters. In Chapter 6, rotational orientation in the OH(X,v=0) photofragments from H2O2 photodissociation using circularly polarized light at 193 nm is observed. Although H2O2 can be excited to both the A and B electronic states by 193 nm, the observed orientation is only related to the A state dynamics. A proposed mechanism about the coupling between a polarized photon and the H2O2 parent rotation is simulated, and the good agreement between the experimental and simulation results further confirms the validity of this mechanism. In Chapter 7, rotational orientation in the NO(X,v) photofragments from NO2 photodissociation using circularly polarized light at 306 nm (v=0,1,2) and at 355 nm (v=0,1) is observed. Two possible mechanisms, the parent molecular rotation and the coherent effect between multiple electronic states, are discussed. NOCl is photodissociated using circularly polarized light at 306 nm, and NO(X,v) rotational distributions (v=0,1) and rotational orientation (v=0) are measured. For the case of NOCl, the generation of orientation is attributed to the coherent effect.
38
Svensson, Pamela H. W. "Everything you wanted to know about the TPA molecule adsorbed on Au(111)." Thesis, Uppsala universitet, Materialteori, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-417648.
Повний текст джерелаАнотація:
The electronic properties of Triphenylamine (TPA) in gas phase and adsorbed on gold(111) have been simulated with Quantum Espresso using Density Functional Theory (DFT). To better understand how the presence of a gold surface affects sunlight absorption in the system, partial Density Of States (pDOS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) of the system have been calculated. To describe the electronic excitation, three different methods have been used, No Core Hole (NCH), Full Core Hole (FCH) and Half Core Hole (HCH) approximation. The excitation of the TPA molecule was made in the nitrogen (N) atom and in the four different carbon (C) atoms with different electronic environments, C-ipso, C-ortho, C-meta and C-para. When using the HCH method, the absorbing atom must be described by a pseudopotential (PP) which includes half of a hole in the 1s orbital. This PP has been generated and a detailed summary of the process is described. The TPA/gold system relaxes to a position with the central N atom of TPA above an gold (Au) atom in the second layer of the surface and at a distance of 3.66 Angstrom, to the first layer. TPA keeps its symmetry with only small differences in the length of atomic bonds when adsorbed. The most striking result of this study is how the band gap of TPA is affected by the gold layer. From the pDOS we can observe that TPA in gas phase has a clear band gap of 2.2 eV with C-ortho dominating in the valence region and the four carbons dominating in the first unoccupied states. When depositing the molecule on the surface of Au(111), the band gap is essentially gone and a number of states appear between the previous highest occupied and lowest unoccupied molecular orbital in TPA. These new states align in energy with three clusters of states of the gold suggesting an interaction between the molecule and the surface. In the generated NEXAFS of nitrogen and carbon in TPA gas phase, one can observe a small pre-peak before the first unoccupied state. This is reinforced when adsorbing the molecule, which generates a pre-peak of approximately 3 eV in width. The pre-peak is connected to the new peaks seen in pDOS, correlating with experimental results on the same system.
39
Feuersenger, Jürgen. "Synthesis and characterisation of 3d-4f-complexes and their magnetic properties." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14195/document.
Повний текст джерелаАнотація:
Ce travail de thèse décrit (i) la synthèse de complexes hétérométalliques d’ions 3d et 4f à partir de précuseurs de Mn, Fe et Co, de sels de lanthanides et de ligands organiques et (ii) l'étude de leurs structures et propriétés. 41 complexes polynucléaires ont été synthétisés dans le cadre de ce travail. Les structures moléculaires de tous les composés ont été déterminées par diffraction des rayons X. Les propriétés magnétiques de 22 complexes ont été étudiées, dont quatre montrent une relaxation lente de leur aimantation considérée comme la signature d’un comportement de molécule-aimant. L'activité catalytique du complexe {Mn4Dy6Li2} calciné a aussi été étudiée et s'est avérée efficace pour l'oxydation du monoxyde de carbone. L'étude systématique de complexes isostructuraux de lanthanides a montré que l'incorporation d’ions 4f peut introduire de l’anisotropie magnétique et que l’ion DyIII est généralement le meilleur candidat pour le ciblage de molécules-aimants hétérométalliques 3d- 4f<br>This dissertation describes the syntheses of 3d-4f-metal complexes starting from preformed compounds of Mn, Fe and Co, lanthanide salts and organic ligands and also the investigation of their structures and properties. 41 new polynuclear heterometallic metal complexes were synthesised in the course of this work with different interesting properties. The structures of all obtained compounds have been confirmed using X-ray diffraction. The magnetic properties of 22 complexes were studied, of which four show frequency dependent out-of-phase signals as expected for SMMs. The catalytic activity of calcinated {Mn4Dy6Li2} was investigated and proved effective for the oxidation of CO. It was established, that the use of precursors leads to new families of compounds. Moreover the study of isostructural compounds across the lanthanide series showed 1) that the incorporation of 4f ions introduces magnetic anisotropy and 2) DyIII is usually the best candidate for targeting 3d-4f-SMMs
40
Krüger, Bastian Christopher [Verfasser], Alec [Akademischer Betreuer] [Gutachter] Wodtke, Dirk [Gutachter] Schwarzer, et al. "From diatomic to polyatomic quantum-state-resolved molecule-surface scattering / Bastian Christopher Krüger ; Gutachter: Alec Wodtke, Dirk Schwarzer, Theofanis Kitsopoulos, Sebastian Kruss, Ricardo Mata, Jörg Schroeder ; Betreuer: Alec Wodtke." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://d-nb.info/114137949X/34.
Повний текст джерела
41
Bezerril, Leonardo Mafra. "Transporte eletr?nico e propriedades termodin?micas de nanobiomol?culas." Universidade Federal do Rio Grande do Norte, 2009. http://repositorio.ufrn.br:8080/jspui/handle/123456789/18614.
Повний текст джерелаАнотація:
Made available in DSpace on 2015-03-03T15:16:23Z (GMT). No. of bitstreams: 1
LeonardoM.pdf: 1880413 bytes, checksum: c785ee7cbc933eb3ac782dc9ac382e6c (MD5)
Previous issue date: 2009-12-18<br>Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico<br>We use a tight-binding formulation to investigate the transmissivity and the currentvoltage (I_V) characteristics of sequences of double-strand DNA molecules. In order to reveal the relevance of the underlying correlations in the nucleotides distribution, we compare theresults for the genomic DNA sequence with those of arti_cial sequences (the long-range correlated Fibonacci and RudinShapiro one) and a random sequence, which is a kind of prototype of a short-range correlated system. The random sequence is presented here with the same _rst neighbors pair correlations of the human DNA sequence. We found that the long-range character of the correlations is important to the transmissivity spectra, although the I_V curves seem to be mostly inuenced by the short-range correlations. We also analyze in this work the electronic and thermal properties along an _-helix sequence obtained from an _3 peptide which has the uni-dimensional sequence (Leu-Glu-Thr- Leu-Ala-Lys-Ala)3. An ab initio quantum chemical calculation procedure is used to obtain the highest occupied molecular orbital (HOMO) as well as their charge transfer integrals, when the _-helix sequence forms two di_erent variants with (the so-called 5Q variant) and without (the 7Q variant) _brous assemblies that can be observed by transmission electron microscopy. The di_erence between the two structures is that the 5Q (7Q) structure have Ala ! Gln substitution at the 5th (7th) position, respectively. We estimate theoretically the density of states as well as the electronic transmission spectra for the peptides using a tight-binding Hamiltonian model together with the Dyson's equation. Besides, we solve the time dependent Schrodinger equation to compute the spread of an initially localized wave-packet. We also compute the localization length in the _nite _-helix segment and the quantum especi_c heat. Keeping in mind that _brous protein can be associated with diseases, the important di_erences observed in the present vi electronic transport studies encourage us to suggest this method as a molecular diagnostic tool<br>Nesta tese, investigamos a transmissividade e as caracter?sticas de corrente como fun??o da diferen?a de potencial, no contexto da liga??o forte, em seq??ncias de dupla fita do DNA. Com o intuito de investigar a relev?ncia das correla??es subjacentes nas distribui??es dos nucleot?deos, comparamos os resultados de uma seq??ncia gen?mica do DNA com duas seq??ncias artificiais (Fibonacci e Rudin-Shapiro, que apresentam correla??o de longo alcance) e uma seq??ncia aleat?ria, prot?tipo de sistemas de correla??o de curto alcance. A seq??ncia aleat?ria utilizada apresenta a mesma correla??o de pares de primeiros vizinhos que a seq??ncia do DNA humano. Observamos que a caracter?stica de correla??o de longo alcance ? importante para o espectro de transmissividade, apesar das curvas IXV serem mais influenciadas por correla??es de curto alcance.
Neste trabalho, analisamos tamb?m as propriedades t?rmicas e eletr?nicas de uma seq?encia α-h?lice, obtida de um pept?deo α3, o qual apresenta a seguinte seq??ncia unidimensional (Leu-Glu-Thr-Leu-Ala-Lys-Ala)3 (estrutura prim?ria). C?lculos ab initio qu?nticos s?o utilizados para obter as energias dos orbitais moleculares mais altos (HOMO, highest occupied molecular orbital), bem como suas integrais de transfer?ncias de cargas quando a seq??ncia α-h?lice forma uma estrutura fibrosa (variante 5Q) e n?o fibrosa (variante 7Q), as quais podem ser observadas atrav?s de microscopia eletr?nica de transmiss?o. A diferen?a entre as duas estruturas ? que a estrutura 5Q (7Q) apresenta a substitui??o Ala → Gln na 5a (7a) posi??o, respectivamente. N?s estimamos, teoricamente, a densidade de estado bem como o espectro de transmiss?o eletr?nico dos pept?deos, utilizando um Hamiltoniano no formalismo da liga??o-forte juntamente com a equa??o de Dyson. Al?m disso, n?s resolvemos a equa??o de Schr?dinger dependente do tempo para obter o espalhamento de um pacote de onda inicialmente localizado. N?s calculamos tamb?m o comprimento de localiza??o e, por fim, o calor espec?fico qu?ntico. Vale lembrar que a forma??o de prote?nas fibrosas podem estar associadas ? doen?as, de forma que as importantes diferen?as observadas no estudo das propriedades eletr?nicas de transporte nos encorajam a sugerir este m?todo como uma ferramenta de diagn?stico molecular
42
Panesar, Kuldeep Singh. "Quantum molecular dynamics of guest molecules in supramolecular complexes." Thesis, University of Nottingham, 2009. http://eprints.nottingham.ac.uk/10741/.
Повний текст джерелаАнотація:
The quantum motion of guest molecules has been studied in a variety of calixarene host-guest complexes, and in a endohedral fullerene complex. The guest molecules of the calixarene complexes studied each comprise weakly hindered methyl groups, which undergo rotation via quantum tunnelling, even at cryogenic temperatures. The rotational motion of the guest methyl-groups has been studied by making temperature and frequency-dependent measurements of proton T1, using field-cycling NMR, thus revealing the spectral density functions of the magnetic dipole-dipole interaction. Crystallographically inequivalent methyl-group environments have been identified and characterised in p-tert-butylcalix[4]arene(1:1)toluene, p-tert-butylcalix[4]arene(1:1)gamma-picoline and p-isopropylcalix[4]arene(2:1)p-xylene. In many of the calixarene complexes the proton spin-lattice relaxation has been observed to be strongly dependent on the thermal history of the sample. Temperature-dependent measurements of proton T1 in samples of p-tert-butylcalix[4]arene(1:1)toluene with partially deuterated guest molecules reveal a systematic reduction in T1 at low temperatures with increased degree of deuteration. Calixarene and fullerene host-guest complexes have been identified as having a potential application in cryogenic MAS-NMR as cryorelaxor complexes, capable of being attached to a large biomolecule and encouraging proton spin-lattice relaxation. The suitability of the calixarene complexes for use in this capacity has been investigated by measuring the temperature-dependence of proton T1 at low temperatures. The quantised rotational and translational motion of dihydrogen confined within an open-cage fullerene—namely, aza-thio-open-cage-fullerene (ATOCF)—has been revealed by inelastic neutron scattering (INS) measurements. The splitting of excited rotational and translational states, due to the low symmetry of the ellipsoidal fullerene cavity, has been directly measured. Assignment of the peaks observed in the INS spectrum has been aided by analysis of the Q-dependence of excitation bands. The thermodynamics of ortho- and parahydryogen have been investigated via temperature dependence measurements. INS measurements have allowed the anistropic rotational potential experienced by the H2 rotor to be determined.
43
Brinne, Roos Johanna. "Reaction dynamics on highly excited states." Doctoral thesis, Stockholms universitet, Fysikum, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-27122.
Повний текст джерелаАнотація:
In this thesis I have performed theoretical studies on the reaction dynamics in few-atom molecules. In particular, I have looked at reaction processes in which highly excited resonant states are involved. When highly excited states are formed, the dynamics becomes complicated and approximations normally used in chemical reaction studies are no longer applicable.To calculate the potential energy curve for some of these states as a function of internuclear distance, a combination of structure calculations and scattering calculations have to be performed, and the reaction dynamics on the potentials has been studied using both time-independent and time-dependent methods.The processes that have been studied and which are discussed in this thesis are ion-pair formation in electron recombination with H3+, dissociative recombination and ion-pair formation of HF+, mutual neutralization in H++F- collisions and dissociative recombination of BeH+. Isotope effects in these reactions have also been investigated. Our calculated cross sections are compared with experimentally measured cross sections for these reactions.
44
Liu, Quan. "Enhanced Emission of a Single Quantum Emitter Coupled to a Microcavity and a Nanocavity." Thesis, Troyes, 2021. http://www.theses.fr/2021TROY0029.
Повний текст джерелаАнотація:
Le développement de techniques basées sur une seule molécule au cours des dernières décennies a permis de sélectionner, de suivre et de mesurer directement une molécule individuelle. Dans cette thèse, la dynamique structurelle d'un seul émetteur quantique, servi par l'hypéricine, est caractérisée. En utilisant la microscopie à balayage confocale combinée à des modes laser polarisés radialement / azimutalement, une réorientation tridimensionnelle du moment dipolaire de transition d'une seule molécule est observée. Pour quantifier les propriétés temporelles de la tautomérie, la fonction d'autocorrélation des photons est utilisée pour extraire les fluctuations d'intensité. Les résultats montrent l'influence distincte de l'environnement local, comme la matrice PVA et l'effet de deutération. L'environnement photonique local d'une molécule est modifié par la microcavité / nanocavité. Un changement significatif du taux d'émission radiatif et des spectres de fluorescence est discuté. Il nous permet de mesurer le rendement quantique absolu en utilisant une microcavité accordable. Les résultats montrent la possibilité de contrôler la tautomérisation en modifiant l'environnement photonique. Par la suite, la dissociation moléculaire est discutée par des spectres Raman améliorés en surface à molécule unique bénéficiant de l'amélioration en champ proche de la nanocavité. Une stratégie d'optimisation expérimentale rapide vers une amélioration optimale de la fluorescence est décrite<br>The development of single molecule-based techniques in the last decades has enabled directly selecting, tracking, and measuring an individual molecule. In this thesis, the structural dynamics of a single quantum emitter, served by hypericin, is characterized. By using confocal scanning microscopy combined with radially/azimuthally polarized laser modes, three-dimensional reorientation of the transition dipole moment of a single molecule is observed. To quantify the temporal properties of the tautomerism, photon autocorrelation function is used to extract the intensity fluctuations. The results show the distinct influence of the local environment, such as PVA matrix and deuteration effect. The local photonic environment of a molecule is modified by the microcavity/nanocavity. A significant change of the radiative emission rate and of the fluorescence spectra is discussed. It allows us to measure the absolute quantum yield by using a tunable microcavity. The results show the possibility of controlling tautomerization by changing the photonic environment. Subsequently, molecular dissociation is discussed by single molecule surface-enhanced Raman spectra profiting from near field enhancement of nanocavity. A fast experimental optimization strategy towards optimal fluorescence enhancement is outlined
45
Ganzhorn, Marc. "Couplage de systèmes magnétiques et mécaniques à échelle moléculaire." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00820247.
Повний текст джерелаАнотація:
Dans ce manuscrit, nous présentons d'abord le bloc de construction moléculaire ultime pour les dispositifs de spintronique, les aimants à molécule unique (Chapitre 2). En particulier, nous nous concentrerons sur une molecule de TbPc2 et différentes approches pour sonder son aimantation à l'aide de détecteurs a base de nanotubes de carbone et de mécanismes de couplage différents (flux magnétique, couplage électronique et mécanique). Dans le but de construire un detecteur de torque supramoléculaire capable de sonder le moment magnétique d'un aimant moléculaire, nous allons décrire dans le chapitre 3 un candidat très prometteur, un système nanoélectromécanique (NEMS) à base d'un nanotube de carbone. Nous décrirons d'abord les avantages de NEMS à base de carbone par rapport aux résonateurs classiques à base de silicium. Par la suite, nous présenterons l'état de l'art des NEMS à base de nanotubes de carbone, en nous focalisant en particulier sur deux différents mouvements nanomécaniques, un mode de flexion transverse et un mode de compression longitudinal. Dans le chapitre 4, nous présenterons la mise en oeuvre expérimentale d'un detecteur de torque supramoléculaire basé sur NEMS à nanotubes de carbone et des aimants à molécule unique. Nous décrirons d'abord le processus de fabrication ultra propre et les étapes de la caractérisation d'un NEMS à nanotubes de carbone à températures ambiante et cryogénique. Nous allons ensuite démontrer un procédé de greffage d'une molécule aimants de TbPc2 sur un tel NEMS à nanotube de carbone, qui conserve à la fois les propriétés magnétiques de la molécule et les propriétés mécaniques du résonateur. Dans le chapitre 5, nous allons ensuite procéder à une étude systématique du mode de flexion transverse dans un NEMS à nanotube de carbone. Nous montrerons, que la dissipation de ce mode de vibration induit par l'effet tunnel d'électron unique à travers le nanotube de carbone (considére comme point quantique) dépend essentiellement de l'environnement électronique du nanotube, c'est à dire de la capacité, du couplage entre le nanotube de carbone et les electrodes métalliqes, du courant et de la température. Les résultats indiquent que l'on pourrait atteindre des facteurs de qualité de 10^6 ou plus en choisissant un diélectrique de grille appropriées et/ou en améliorant le couplage entre le nanotube de carbone et les electrodes, ce qui permettrait notamment d'augmenter la sensibilité du NEMS nanotubes de carbone par rapport à un torque magnétique générer par le retournement d'un aimant moléculaire. Dans le chapitre 6, nous démontrons la présence d'un mode de vibration longitudinal quantique dans un NEMS à base de nanotube de carbon fonctionnalisé avec des aimants moléculaires de TbPc2. Nous allons en particulier montrer que la nature quantique des deux systèmes, se traduit par un fort couplage entre le mode de compression longitudinal et l'aimantation d'un aimant moléculaire TbPc2 unique greffé sur la parois du nanotube de carbone. Ce fort couplage permet par la suite de détecter les états de spin nucléaire dans la molécule de TbPc2. Enfin, nous présenterons dans la conclusion de ce manuscrit quelques perspectives pour la détection et la manipulation (coherente) d'un seul spin (nucléaire) à l'aide d'un système mécanique quantique.
46
Orlando, A. M. "NEW INSIGHT IN ELECTRON DENSITY AND ELECTRON SPIN DENSITY THROUGH TOPOLOGICAL DESCRIPTORS BASED ON BADER'S THEORY OF ATOM IN MOLECULES." Doctoral thesis, Università degli Studi di Milano, 2016. http://hdl.handle.net/2434/374929.
Повний текст джерелаАнотація:
This Ph.D. thesis is focused on the application of quantum theory of atoms in molecules (QTAIM) based chemical descriptors to challenging chemical test-cases, as well as on the development of novel topological descriptors, like the Source Function for the spin density. The thesis is organized as follows: In chapter 1 the electron density (ED) of a very unusual structural feature in a synthetic beta–sultamic analogue (DTC), has been explored by both low-T single–crystal X–ray diffraction and quantum mechanical simulations to gain insights into the subtle interplay between structure, electron delocalization and crystal field polarization effects. The core chemical moiety in DTC is an uncommon 4–membered thiazete–1,1–dioxide heterocycle, where the formally single N–C bond is, on average, 0.018 Å shorter than the formally double N=C bond. Both local and non–local topological descriptors provided by QTAIM have been employed in the analysis of DTC in comparison with chemically related derivatives and possible implications from the viewpoint of the accurate in silico modelling of crystal structures are discussed. Particular attention is dedicated on such kind of issues in chemical and pharmaceutical industries, because the control of the crystal structure is really problematic in some cases; in fact different polymorphs of the same substance have different intensive physical properties, such as solubility, refraction index and conductivity and problems may arise in industrial processes related to the synthesis of chemicals and drugs on large scale. In chapter 2, we focused on the source function (SF) QTAIM based topological descriptor. The electron density (ED) at any point r within a system may be regarded as consisting of a sum of SF contributions S(r; X) representing a measure of how the various atomic basins (X) or groups of atomic basins defined through QTAIM contribute to determine the ρ(r) at r. Recently it was shown that the SF is able to reveal electron delocalization effects in planar electron conjugated systems, in terms of an increased capability of determining the ED along a given bond by the distant, though through-bonds connected, atomic basins and, at the same time, into a decreased ability to do so by the two atoms directly involved in the bond. Such an adjustment of sources then translates into a pictorial pattern of enhanced and reduced atomic SF contributions from, respectively, distant and nearby atoms, compared to the case of a partially or fully saturated network of bonds. Then we have extended such an analysis to the non planar conjugated systems, where the usual electron separation does no longer apply. Being based on the total ED, the SF analysis may be safely applied also in these less conventional electron delocalized systems. In the present Ph. D. thesis we have extended the SF reconstruction approach also to the electron density spin counterparts in vacuo. Such reconstruction was investigated both on simple (but chemically meaningful) spin-polarized molecular systems and on more complex single-molecule magnets. This investigation has showed that the difference between the two spin counterparts of electron density distribution can be reconstructed with a sufficient accuracy, analogously to the case of the total ED. Moreover, it was found that the SF for the electron spin density brings in precious chemical information, neatly distinguishing the quite different roles played by the unpaired electrons ED and the spin polarized ED due to the remaining electrons. Furthermore, quantitative answers to questions related to the transferability of the spin density in alkyl radicals or to the transmission of spin information in metal(s)-ligand systems were provided. Understanding, from a real space perspective, by which mechanisms spin information transmits, might be of relevance to interpret the fundamental magnetic interactions present in complex materials, such as for example coordination polymers or Heussler and half-Heussler alloys. As these interactions have a key role in spintronics, characterization of the chemical bond and interpretation of the electron spin density distributions in these systems through the SF analysis, could hopefully disclose structure-property relationships extremely useful for the design of materials with particular physical properties.
47
Дорошенко, Дмитро Юрійович, Дмитрий Юрьевич Дорошенко, Dmytro Yuriiovych Doroshenko, Анатолій Іванович Рубан, Анатолий Иванович Рубан та Anatolii Ivanovych Ruban. "Исследование вольт-амперных характеристик и квантовой проводимости органических молекул бензол-ди-тиола и ферроцена". Thesis, Сумский государственный университет, 2014. http://essuir.sumdu.edu.ua/handle/123456789/39661.
Повний текст джерелаАнотація:
В данной работе методом разрыва перехода проведено экспериментальное исследование вольтмперных характеристик и квантовой проводимости органических молекул бензол-ди-тиола и ферроцена. В
данном случае проводился разрыв металлических золотых контактов с повторным их соединением в присутствии исследуемой молекулы. Этот принцип основан на предположении, что молекула, которая связывается с металлической поверхностью, будет с некоторой конечной вероятностью образовывать проводящий мост между электродами.
48
Rossi, François-Noël. "Etude théorique des collisions non réactives entre atomes alcalins et molécules d'hydrogène ou de deuterium : Calcul et analyse des surfaces de potentiel, application aux transitions de structure fine du rubidium." Paris 13, 1986. http://www.theses.fr/1986PA132015.
Повний текст джерелаАнотація:
Calcul des courbes de potentiel adiabatiques pour les géométries colinéaires et perpendiculaires, à l'aide d'un pseudopotentiel dépendant du moment orbital électronique et d'une approche à deux centres; bon accord avec les calculs ab initio existants. Examen des différentes symétries de ces systèmes dans le formalisme de la théorie des groupes, afin d'étudier les valeurs propres et facteurs propres de l'hamiltonien électronique. Calcul quantique des sections efficaces relatives des transitions de structure fine de Rb induites par collision avec H(2) ou D(2). En tenant compte des niveaux rotationnels moléculaires, obtention d'un très bon accord avec les résultats expérimentaux et interprétation de l'effet isotopique
49
Tekin, Emine Deniz. "Investigation Of Biologically Important Small Molecules: Quantum Chemical And Molecular Dynamics Calculations." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612343/index.pdf.
Повний текст джерелаАнотація:
In this thesis, six small molecules (S-allylcysteine, S-allyl mercaptocysteine, allicin, methyl propyl disulfide, allyl methyl sulfide and dipropylsulfide) that are found in garlic and onion, and are known to be beneficial for human health were studied using molecular mechanics, semi-empirical methods, ab-initio (Restricted Hartree Fock), and density functional theory. Using the same methods, a synthetic pyrethroid pesticide molecule, called cyfluthrin, was also studied. Structural, vibrational and electronic properties of these molecules were found. These theoretical studies could clarify the role of these molecules on human health before they are commercially developed and used. In addition, unfolding dynamics of small peptide sequences (DDATKTFT and its variants) in immunoglobulin G-binding protein G was investigated. Protein folding and unfolding is one of the most important unsolved problems in molecular biology. Because of the large number of atoms involved in protein folding, it is a massive computational problem. The hope is that, one could understand this mechanism with the help of molecular dynamics simulation on small peptides. One of our findings is that the location of the hydrogen bonds is important for the stability of the peptide.
50
Urdampilleta, Matias. "Spintronique moléculaire de la vanne de spin à la détection d'un spin unique." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00770488.
Повний текст джерелаАнотація:
Spintronique moléculaire : de la vanne de spin à la détection d'un spin unique. Parmi les thématiques qui ont émergé ces dix dernières années, la spintronique moléculaire est intéressante de par son caractère hybride, à la croisée entre l'électronique de spin, l'électronique moléculaire et le magnétisme moléculaire. Dans ce nouveau domaine, on cherche à exploiter les propriétés magnétiques et quantiques des aimants moléculaires pour créer des dispositifs originaux, utiles en spintronique ou en information quantique. Mon projet de thèse s'inscrit dans cette perspective en voulant combiner un transistor à nanotube de carbone avec des aimants à molécule unique, en les couplant par des interactions supramoléculaires. L'objectif est d'observer le renversement magnétique d'une seule molécule par des mesures de transport électronique à travers le nanotube. En effet, le diamètre de ce dernier étant comparable aux dimensions d'un aimant moléculaire, le couplage devrait être suffisamment fort pour en permettre la détection. La réalisation d'un tel dispositif, un défi technique, et la question de savoir s'il était réellement possible de détecter et de caractériser le moment d'une seule molécule ont constitué les deux enjeux majeurs de cette thèse. Une grande partie du travail réalisé porte sur la fabrication du dispositif expérimental par des techniques de micro- et nano-fabrication, ainsi que sur l'optimisation du greffage des aimants moléculaires sur la surface du nanotube. Dans un second temps, nous nous intéressons à l'étude du système et à son comportement à très basse température (100 mK). En effet, la proximité des aimants moléculaires TbPc2 modifie de façon spectaculaire les propriétés de transport d'un nanotube. En particulier, nous présentons la réalisation d'un dispositif dont la réponse est analogue à une vanne de spin classique, où les molécules magnétiques jouent le rôle de polariseur ou d'analyseur de spin. Grâce à ce système, nous avons réussi à affiner nos connaissances sur TbPc2. Entre autres résultats, nous sommes parvenus à isoler et à caractériser le retournement du moment magnétique d'un seul ion de terbium. Enfin, la dernière partie de cette thèse est consacrée à l'étude de l'interaction hyperfine au sein du terbium. En réalisant un dispositif qui n'est couplé qu'à deux molécules, nous avons mis en évidence qu'il est possible de réaliser une lecture directe de l'état d'un spin nucléaire unique.