Articles de revues : « Quantum molecule »

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Fatma Gen, Fatma Gen, et Hanan Bsehen and Fatma Kandemirli Hanan Bsehen and Fatma Kandemirli. « Quantum Chemical Studies of Carbazochrome Molecule ». Journal of the chemical society of pakistan 44, n^o 2 (2022) : 109. http://dx.doi.org/10.52568/000997/jcsp/44.02.2022.

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Control of spontaneous and postoperative bleeding is of particular concern to surgeons, anesthetists, hematologists, and the patient. Mainly carbazochrome(2-(1,2,3,6-tetrahydro-3-hydroxy-1-methyl-6-oxo-5H-indol-5-ylidene)-hydrazinecarboxamide,CBZ), adrenochrome derivative, currently used as hemostatic drugs. With Density Functional Theory (DFT), at B3LYP level with 6–311G(d,p), 6–311+G(d,p), 6–311++G(d,p), 6–311++G(2d,2p), 6-311++G(3df,3pd) basis sets. Molecular structure of carbazochrome (C10H12N4O3) in the basic state in gas phase and solvent (ethanol, N, N-dimethyl form amide, N, N-dimethyl sulfoxide, water ) phases, energy Parameters such as the lowest empty molecular orbital (ELUMO), the highest energy filled molecular orbital (EHOMO), the energy difference between ELUMO and EHOMO, hardness, softness, electrophilicity index, chemical potential, electrofugality and nucleofugality were calculated and its effect on carbazochrome molecule has been investigated. In this study, the stabilization energy and hybridization of carbazochrome optimized by using DFT with B3LYP/6-311G(d, p) level in gas phase solvent phase, using natural bond orbital theory as integrated with NBO 3.1 were studied. Quantum mechanical calculations by using time-dependent DFT at B3LYP level 6–311G(d,p), 6–311+G(d,p), 6–311++G(d,p), 6–311++G(2d,2p), 6-311++G(3df,3pd) basis sets were performed to obtain some valuable information about the UV spectrum of the carbazochrome molecule in gas and solvent medium (ethanol, N, N-dimethylformamide, N, N-dimethylsulfoxide, water) and compared with experimental values. Based on Gaussianand#39;s output data, on the basis of vibration analysis and statistical thermodynamics, standard thermodynamicfunctions of the carbazochrome molecule at different temperatures (200oC-1000oC): thermodynamic properties such as heat capacity entropy, enthalpy, Gibbs free energy were calculated and the effect of base sets and solvent on these properties was investigated.

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Liza, Nishattasnim, Dylan Murphey, Peizhong Cong, David W. Beggs, Yuihui Lu et Enrique P. Blair. « Asymmetric, mixed-valence molecules for spectroscopic readout of quantum-dot cellular automata ». Nanotechnology 33, n^o 11 (21 décembre 2021) : 115201. http://dx.doi.org/10.1088/1361-6528/ac40c0.

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Abstract Mixed-valence compounds may provide molecular devices for an energy-efficient, low-power, general-purpose computing paradigm known as quantum-dot cellular automata (QCA). Multiple redox centers on mixed-valence molecules provide a system of coupled quantum dots. The configuration of mobile charge on a double-quantum-dot (DQD) molecule encodes a bit of classical information robust at room temperature. When arranged in non-homogeneous patterns (circuits) on a substrate, local Coulomb coupling between molecules enables information processing. While single-electron transistors and single-electron boxes could provide low-temperature solutions for reading the state of a ∼1 nm scale molecule, we propose a room-temperature read-out scheme. Here, DQD molecules are designed with slightly dissimilar quantum dots. Ab initio calculations show that the binary device states of an asymmetric molecule have distinct Raman spectra. Additionally, the dots are similar enough that mobile charge is not trapped on either dot, allowing device switching driven by the charge configuration of a neighbor molecule. A technique such as tip-enhanced Raman spectroscopy could be used to detect the state of a circuit comprised of several QCA molecules.

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Takatsuka, Kazuo. « Quantum Chaos in the Dynamics of Molecules ». Entropy 25, n^o 1 (29 décembre 2022) : 63. http://dx.doi.org/10.3390/e25010063.

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Quantum chaos is reviewed from the viewpoint of “what is molecule?”, particularly placing emphasis on their dynamics. Molecules are composed of heavy nuclei and light electrons, and thereby the very basic molecular theory due to Born and Oppenheimer gives a view that quantum electronic states provide potential functions working on nuclei, which in turn are often treated classically or semiclassically. Therefore, the classic study of chaos in molecular science began with those nuclear dynamics particularly about the vibrational energy randomization within a molecule. Statistical laws in probabilities and rates of chemical reactions even for small molecules of several atoms are among the chemical phenomena requiring the notion of chaos. Particularly the dynamics behind unimolecular decomposition are referred to as Intra-molecular Vibrational energy Redistribution (IVR). Semiclassical mechanics is also one of the main research fields of quantum chaos. We herein demonstrate chaos that appears only in semiclassical and full quantum dynamics. A fundamental phenomenon possibly giving birth to quantum chaos is “bifurcation and merging” of quantum wavepackets, rather than “stretching and folding” of the baker’s transformation and the horseshoe map as a geometrical foundation of classical chaos. Such wavepacket bifurcation and merging are indeed experimentally measurable as we showed before in the series of studies on real-time probing of nonadiabatic chemical reactions. After tracking these aspects of molecular chaos, we will explore quantum chaos found in nonadiabatic electron wavepacket dynamics, which emerges in the realm far beyond the Born-Oppenheimer paradigm. In this class of chaos, we propose a notion of Intra-molecular Nonadiabatic Electronic Energy Redistribution (INEER), which is a consequence of the chaotic fluxes of electrons and energy within a molecule.

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Tamulis, Arvydas, Vykintas Tamulis et Aiste Ziriakoviene. « Quantum Mechanical Design of Molecular Computers Elements Suitable for Self-Assembling to Quantum Computing Living Systems ». Solid State Phenomena 97-98 (avril 2004) : 173–80. http://dx.doi.org/10.4028/www.scientific.net/ssp.97-98.173.

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There are presented logic gates of molecular electronics digital computers. Maximal length of these molecular electronics digital logic gates are no more than four nanometers and maximal width 2.5 nm. The results of light induced internal molecular motions in azo-dyes molecules have been used for the design of light driven logically controlled (OR, AND) molecular machines composed from organic photoactive electron donor dithieno[3,2-b:2',3'-d]thiophene and ferrocene molecules, electron accepting tetracyano-indane molecule, and moving azo-benzene molecular fragment. Density functional theory (DFT) B3PW91/6-311G model calculations were performed for the geometry optimization of these molecular electronics logical gates. Applied DFT time dependent (DFT-TD/B3PW91) method and our visualization program give absorption spectra of designed molecular gates and show from which fragments electrons are hopping in various excited states. Quantum mechanical investigations of proton Nuclear Magnetic Resonance (NMR) values of Cu, Co, Zn, Mn and Fe biliverdin derivatives and their dimers using ab initio Hartree-Fock (HF) and DFT methods indicate that these modified derivatives should generate from one to twelve Quantum Bits (QuBits). The chemical shifts are obtained as the difference of the values of the tetramethylsilane (Si(CH3)4) molecule Gauge-Independent Atomic Orbital (GIAO) nuclear magnetic shielding tensor on the hydrogen atoms and that of the magnetically active molecules. There are designed several single supermolecule and supramolecular devices containing molecular electronics digital logic gates, photoactive molecular machines and elements of molecular NMR quantum computers that allowed to design several supramolecular Control NOT NMR quantum computing gates. Self-assembling simulations of these molecular quantum computing gates induced idea of self-assembled molecular quantum supercomputer and molecular quantum computing life.

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TACHIKAWA, MASANORI, et MOTOYUKI SHIGA. « AB INITIO PATH INTEGRAL STUDY ON ISOTOPE EFFECT OF AMMONIA MOLECULE ». Journal of Theoretical and Computational Chemistry 04, n^o 01 (mars 2005) : 175–81. http://dx.doi.org/10.1142/s0219633605001337.

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We have applied ab initio path integral molecular dynamics simulation to study the quantum feature and proton/deuteron isotope effect of ammonia molecule. This method treats all the rotational and vibrational degrees of freedom fully quantum mechanically, while the potential energies of the respective molecular configurations are calculated "on the fly" using ab initio quantum chemical approach. The differences on the geometry and the electronic structure between NH 3 and ND 3 molecules are investigated in detail.

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Lozovik, Yu E., et N. E. Kaputkina. « Quantum Dot “Molecule” ». Physica Scripta 57, n^o 4 (1 avril 1998) : 542–44. http://dx.doi.org/10.1088/0031-8949/57/4/013.

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Mörschel, Philipp, et Martin U. Schmidt. « Prediction of molecular crystal structures by a crystallographic QM/MM model with full space-group symmetry ». Acta Crystallographica Section A Foundations and Advances 71, n^o 1 (1 janvier 2015) : 26–35. http://dx.doi.org/10.1107/s2053273314018907.

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A crystallographic quantum-mechanical/molecular-mechanical model (c-QM/MM model) with full space-group symmetry has been developed for molecular crystals. The lattice energy was calculated by quantum-mechanical methods for short-range interactions and force-field methods for long-range interactions. The quantum-mechanical calculations covered the interactions within the molecule and the interactions of a reference molecule with each of the surrounding 12–15 molecules. The interactions with all other molecules were treated by force-field methods. In each optimization step the energies in the QM and MM shells were calculated separately as single-point energies; after adding both energy contributions, the crystal structure (including the lattice parameters) was optimized accordingly. The space-group symmetry was maintained throughout. Crystal structures with more than one molecule per asymmetric unit,e.g.structures withZ′ = 2, hydrates and solvates, have been optimized as well. Test calculations with different quantum-mechanical methods on nine small organic molecules revealed that the density functional theory methods with dispersion correction using the B97-D functional with 6-31G* basis set in combination with the DREIDING force field reproduced the experimental crystal structures with good accuracy. Subsequently the c-QM/MM method was applied to nine compounds from the CCDC blind tests resulting in good energy rankings and excellent geometric accuracies.

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Yao, Jie, et Ai-Di Zhao. « Advances in detection and regulation of surface-supported molecular quantum states ». Acta Physica Sinica 71, n^o 6 (2022) : 060701. http://dx.doi.org/10.7498/aps.71.20212324.

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Single molecular systems are typical quantum confinement systems, which have rich electronic states, photon states and spin states due to their discrete energy levels, localized orbitals and diverse chemical structures. The states determined by quantum mechanics in these molecular systems make it possible to serve as great physical entities for future quantum information technology. The detection and manipulation of quantum states on a single molecule scale are beneficial to the bottom-up construction of quantum devices. Owing to the highly limited spatial localization of single molecular systems, it is difficult to accurately address and manipulate them with conventional macroscopic characterization methods. Scanning tunneling microscope (STM) is such a powerful tool that it can achieve high-resolution real-space imaging as well as spectroscopic investigation, with the ability to <i>in-situ</i> manipulating the individual atoms or molecules. It can also work jointly with various near-field or external field characterization techniques, making it a most important technique for precisely detecting and manipulating quantum properties at a single molecule level. In this paper, we review recent research progress of quantum states of surface-supported single molecules and relevant structures based on scanning tunneling microscopy. We start from the methods for the synthesis of molecular structures with desired quantum states, and then we review the recent advances in the local spin states for single molecular systems and the optical properties of single molecules serving as a single-photon source. An emerging family of molecular nanographene systems showing intriguing topological properties and magnetic properties is also reviewed. In the last part, we summarize the research progress made recently and prospect the future development of the quantum states at a single molecular level.

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Sinhal, Mudit, Ziv Meir, Kaveh Najafian, Gregor Hegi et Stefan Willitsch. « Quantum-nondemolition state detection and spectroscopy of single trapped molecules ». Science 367, n^o 6483 (12 mars 2020) : 1213–18. http://dx.doi.org/10.1126/science.aaz9837.

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Trapped atoms and ions, which are among the best-controlled quantum systems, find widespread applications in quantum science. For molecules, a similar degree of control is currently lacking owing to their complex energy-level structure. Quantum-logic protocols in which atomic ions serve as probes for molecular ions are a promising route for achieving this level of control, especially for homonuclear species that decouple from blackbody radiation. Here, a quantum-nondemolition protocol on single trapped N2+ molecules is demonstrated. The spin-rovibronic state of the molecule is detected with >99% fidelity, and a spectroscopic transition is measured without destroying the quantum state. This method lays the foundations for new approaches to molecular spectroscopy, state-to-state chemistry, and the implementation of molecular qubits.

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MAITI, SANTANU K., et S. N. KARMAKAR. « QUANTUM TRANSPORT THROUGH HETEROCYCLIC MOLECULES ». International Journal of Modern Physics B 23, n^o 02 (20 janvier 2009) : 177–87. http://dx.doi.org/10.1142/s021797920904970x.

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We explore electron transport properties in molecular wires made of heterocyclic molecules (pyrrole, furan and thiophene) by using the Green's function technique. Parametric calculations are given based on the tight-binding model to describe the electron transport in these wires. It is observed that the transport properties are significantly influenced by (a) the heteroatoms in the heterocyclic molecules and (b) the molecule-to-electrodes coupling strength. Conductance (g) shows sharp resonance peaks associated with the molecular energy levels in the limit of weak molecular coupling, while they get broadened in the strong molecular coupling limit. These resonances get shifted with the change of the heteroatoms in these heterocyclic molecules. All the essential features of the electron transfer through these molecular wires become much more clearly visible from the study of our current-voltage (I-V) characteristics, and they provide several key information in the study of molecular transport.

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Wang, Bing-Wu, Zhe-Ming Wang et Song Gao. « Organometallic Single-Ion Magnets ». Acta Crystallographica Section A Foundations and Advances 70, a1 (5 août 2014) : C274. http://dx.doi.org/10.1107/s2053273314097253.

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The single-molecule magnets (SMMs) are attracting the increasing interesting due to their potential applications in high density information storage, quantum computing, molecular spintronics, and magnetic refrigeration. This field provides scientists a possible access into the crossover of the classical and quantum world, and a wonderful model to study the fascinating magnetic properties between microscopic and macroscopic materials, such as slow magnetization relaxation and quantum tunneling effect. After the milestone discovery of the first single-molecule magnets (SMMs) Mn12ac, many new SMMs were structurally and magnetically characterized. The most studied systems are mainly traditional coordination compounds with polynuclear structures. However, for the difficulties in the control of magnetic anisotropy and exchange coupling interactions of the cluster-type molecules, Mn12ac molecule is still one of the most important SMMs with the high relaxation barrier. From 2011 [1-3], we explored an organometallic sandwich molecule, Cp*ErCOT(Cp* = pentamethylcyclopenta-dienide; COT = cyclooctatetraenide), which behaves as a single-ion magnets, into the field of molecular nanomagnets. It opened a door of SMMs to the chemists in organometallic chemistry. Recently, we found some new sandwich or half-sandwich lanthanide organometallic molecules could also show the slow relaxation of magnetization. We hope these systems can provide new understandings of slow magnetic relaxation and new clues on the design and synthesis of molecular nanomagnets. This work was supported by NSFC, the National Basic Research Program of China.

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LUO, YUAN, LAN LUO, KAI SUN, MIN-LONG TAO et JUN-ZHONG WANG. « STM STUDY OF THE ADSORPTION OF SINGLE-MOLECULE MAGNET Fe4 ON Bi(111) SURFACE ». Surface Review and Letters 22, n^o 05 (27 août 2015) : 1550060. http://dx.doi.org/10.1142/s0218625x15500602.

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Single-molecule magnets (SMMs) have unique magnetic properties such as quantum tunneling of magnetization and quantum coherent oscillation, which have potential applications in quantum computation and information storage. In this paper, using the tip-deposition method, we have grafted individual Fe 4 molecules onto the semi-metallic Bi (111) surface. Low temperature scanning tunneling microscope (LT-STM) was used to characterize the molecular morphology and electronic structures. It was found that individual Fe 4 molecules reveal a triangle shape, which is consistent with the molecular structure of Fe 4. Scanning tunneling spectroscopy (STS) analysis indicated that the HOMO–LUMO gap is 0.49 eV. These studies provide direct information about the adsorption of individual SMMs on semi-metal surfaces.

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Sinhal, Mudit, Ziv Meir et Stefan Willitsch. « Non-destructive State Detection and Spectroscopy of Single Molecules ». CHIMIA International Journal for Chemistry 75, n^o 4 (28 avril 2021) : 291–95. http://dx.doi.org/10.2533/chimia.2021.291.

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We review our recent experimental results on the non-destructive quantum-state detection and spectroscopy of single trapped molecules. At the heart of our scheme, a single atomic ion is used to probe the state of a single molecular ion without destroying the molecule or even perturbing its quantum state. This method opens up perspectives for new research directions in precision spectroscopy, for the development of new frequency standards, for tests of fundamental physical concepts and for the precise study of chemical reactions and molecular collisions with full control over the molecular quantum state.

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Yamashita, Masahiro. « Frontier of Quantum Molecular Spintronics Based on Single-Molecule Quantum Magnets ». Bulletin of Japan Society of Coordination Chemistry 65 (2015) : 2–8. http://dx.doi.org/10.4019/bjscc.65.2.

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Liao, Kun, Xiaoyong Hu, Tianyi Gan, Qihang Liu, Zhenlin Wu, Chongxiao Fan, Xilin Feng, Cuicui Lu, Yong-chun Liu et Qihuang Gong. « Photonic molecule quantum optics ». Advances in Optics and Photonics 12, n^o 1 (6 mars 2020) : 60. http://dx.doi.org/10.1364/aop.376739.

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Browne, Cormac, Tristan Farrow, Oscar C. O. Dahlsten, Robert A. Taylor et Vedral Vlatko. « Organic molecule fluorescence as an experimental test-bed for quantum jumps in thermodynamics ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 473, n^o 2204 (août 2017) : 20170099. http://dx.doi.org/10.1098/rspa.2017.0099.

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We demonstrate with an experiment how molecules are a natural test bed for probing fundamental quantum thermodynamics. Single-molecule spectroscopy has undergone transformative change in the past decade with the advent of techniques permitting individual molecules to be distinguished and probed. We demonstrate that the quantum Jarzynski equality for heat is satisfied in this set-up by considering the time-resolved emission spectrum of organic molecules as arising from quantum jumps between states. This relates the heat dissipated into the environment to the free energy difference between the initial and final state. We demonstrate also how utilizing the quantum Jarzynski equality allows for the detection of energy shifts within a molecule, beyond the relative shift.

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JOACHIM, C., I. DUCHEMIN, J. FIURÁŠEK et N. J. CERF. « HAMILTONIAN LOGIC GATES : COMPUTING INSIDE A MOLECULE ». International Journal of Nanoscience 04, n^o 01 (février 2005) : 107–18. http://dx.doi.org/10.1142/s0219581x05002948.

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Using an intramolecular single-electron transfer process, we show how computing inside a quantum system can be performed using the time evolution driven by the preparation of the system in a nonstationary state. The molecule Hamiltonian is separated in three parts: the input, calculation, and output parts. Two optimization procedures are described in order to design an efficient monoelectronics level structure for molecular logic gates. An XOR gate and a half-adder using six electronic quantum levels are presented in a prospect to integrate a full logic gate inside a single molecule without forcing the molecule to have the shape of an electrical circuit. We foresee the merger of molecular electronics with quantum computation at the nanoscale.

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Li, Rui-Hao, Jun-Yang Liu et Wen-Jing Hong. « Regulation strategies based on quantum interference in electrical transport of single-molecule devices ». Acta Physica Sinica 71, n^o 6 (2022) : 067303. http://dx.doi.org/10.7498/aps.71.20211819.

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The quantum interference effect in single-molecule devices is a phenomenon in which electrons are coherently transported through different frontier molecular orbitals with multiple energy levels, and the interference will occur between different energy levels. This phenomenon results in the increase or decrease of the probability of electron transmission in the electrical transport of the single-molecule device, and it is manifested in the experiment when the conductance value of the single-molecule device increases or decreases. In recent years, the use of quantum interference effects to control the electron transport in single-molecule device has proved to be an effective method, such as single-molecule switches, single-molecule thermoelectric devices, and single-molecule spintronic devices. In this work, we introduce the related theories of quantum interference effects, early experimental observations, and their regulatory role in single-molecule devices.

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Suponitsky, Kyrill, et Tatiana Timofeeva. « Hyperpolarizability of 6-vertex carboranes quantum chemical study ». Open Chemistry 1, n^o 1 (1 mars 2003) : 1–9. http://dx.doi.org/10.2478/bf02479253.

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AbstractStructure and molecular first hyperpolarizability (β) of nitro-amino-substituted 6-vertex 1,6-carboranes are investigated by means of DFT calculations. The results obtained have revealed that the relative orientation of substituents with respect to the carborane cage influences bond lengths distribution in the cage, which leads to significant changes in the values of hyperpolarizabilities. Calculations with different basis sets have demonstrated that the value of β is not significantly affected by the choice of basis set. The calculated data shows that hyperpolarizability of carborane molecules substituted for carbon atoms is lower than when substituted for boron atoms. For latter molecule, the value of β is of the same order as that of para-nitroaniline molecule.

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He, Xiaodong, Kunpeng Wang, Jun Zhuang, Peng Xu, Xiang Gao, Ruijun Guo, Cheng Sheng et al. « Coherently forming a single molecule in an optical trap ». Science 370, n^o 6514 (24 septembre 2020) : 331–35. http://dx.doi.org/10.1126/science.aba7468.

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Ultracold single molecules have wide-ranging potential applications, such as ultracold chemistry, precision measurements, quantum simulation, and quantum computation. However, given the difficulty of achieving full control of a complex atom-molecule system, the coherent formation of single molecules remains a challenge. Here, we report an alternative route to coherently bind two atoms into a weakly bound molecule at megahertz levels by coupling atomic spins to their two-body relative motion in a strongly focused laser with inherent polarization gradients. The coherent nature is demonstrated by long-lived atom-molecule Rabi oscillations. We further manipulate the motional levels of the molecules and measure the binding energy precisely. This work opens the door to full control of all degrees of freedom in atom-molecule systems.

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Petrov, Victor, et Marta Avilova. « Theoretical Investigations of the Interaction of Gaseous Pollutants Molecules with the Polyacrylonitrile Surface ». Chemosensors 6, n^o 3 (13 septembre 2018) : 39. http://dx.doi.org/10.3390/chemosensors6030039.

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This work presents theoretical studies of the interaction of molecules of several gaseous pollutants with polyacrylonitrile (PAN) surface in the presence of a water and/or oxygen molecule. For this purpose, a PAN cluster model has been proposed by the methods of quantum chemical calculations and molecular modeling. The energy-favorable positions, in which the gas molecules are located relative to the surface of the PAN cluster, are determined and the thermodynamic and the following geometric parameters of the systems are calculated: “PAN cluster − oxygen molecule”, “PAN cluster − oxygen molecule − gas molecule”, “PAN cluster − water molecule − molecule of oxygen”, and “PAN cluster − a molecule of water − an oxygen molecule − a gas molecule”. It is concluded that PAN in atmospheric air in the presence of oxygen molecules is sensitive to carbon oxide (IV), sulfur (IV) oxide, chlorine, hydrogen sulfide and carbon oxide (II). In an anoxic environment, PAN films will show selective sensitivity to chlorine. The presence of water molecules in the investigated air should not affect the gas sensitivity of PAN films.

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Levitt, Malcolm H. « Spectroscopy of light-molecule endofullerenes ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 371, n^o 1998 (13 septembre 2013) : 20120429. http://dx.doi.org/10.1098/rsta.2012.0429.

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Molecular endofullerenes are supramolecular systems consisting of fullerene cages encapsulating small molecules. Although most early examples consist of encapsulated metal clusters, recently developed synthetic routes have provided endofullerenes with non-metallic guest molecules in high purity and macroscopic quantities. The encapsulated light molecule behaves as a confined quantum rotor, displaying rotational quantization as well as translational quantization, and a rich coupling between the translational and rotational degrees of freedom. Furthermore, many encapsulated molecules display spin isomerism. Spectroscopies such as inelastic neutron scattering, nuclear magnetic resonance and infrared spectroscopy may be used to obtain information on the quantized energy level structure and spin isomerism of the guest molecules. It is also possible to study the influence of the guest molecules on the cages, and to explore the communication between the guest molecules and the molecular environment outside the cage.

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Slota, Michael, et Lapo Bogani. « Combining Molecular Spintronics with Electron Paramagnetic Resonance : The Path Towards Single-Molecule Pulsed Spin Spectroscopy ». Applied Magnetic Resonance 51, n^o 11 (novembre 2020) : 1357–409. http://dx.doi.org/10.1007/s00723-020-01292-0.

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AbstractWe provide a perspective on how single-molecule magnets can offer a platform to combine quantum transport and paramagnetic spectroscopy, so as to deliver time-resolved electron paramagnetic resonance at the single-molecule level. To this aim, we first review the main principles and recent developments of molecular spintronics, together with the possibilities and limitations offered by current approaches, where interactions between leads and single-molecule magnets are important. We then review progress on the electron quantum coherence on devices based on molecular magnets, and the pulse sequences and techniques necessary for their characterization, which might find implementation at the single-molecule level. Finally, we highlight how some of the concepts can also be implemented by including all elements into a single molecule and we propose an analogy between donor–acceptor triads, where a spin center is sandwiched between a donor and an acceptor, and quantum transport systems. We eventually discuss the possibility of probing spin coherence during or immediately after the passage of an electron transfer, based on examples of transient electron paramagnetic resonance spectroscopy on molecular materials.

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Wei, Bolin, Zhong Cao et Bo Cui. « Atom-molecule conversion with quantum manipulations ». Modern Physics Letters B 34, n^o 30 (3 août 2020) : 2050337. http://dx.doi.org/10.1142/s0217984920503376.

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In this paper, we investigate quantum manipulations in an open atom-molecule conversion system. Through the transformation for the basis of the system, a set of time-dependent equations are derived under mean field approximation. We find that transitions between different dynamic areas of the system can be realized through manipulating an external rotating magnetic field, which corresponds to the tunneling rate in the equation. Through investigating the phase space of the system, we design an efficient method to combine pure cold molecule and pure molecular state so that it can be reached with much shorter time. Furthermore, manipulation of laser signal modulation, external diving and the distance-selective diffusion are also discussed in this paper.

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Mitra, Debayan, Nathaniel B. Vilas, Christian Hallas, Loïc Anderegg, Benjamin L. Augenbraun, Louis Baum, Calder Miller, Shivam Raval et John M. Doyle. « Direct laser cooling of a symmetric top molecule ». Science 369, n^o 6509 (10 septembre 2020) : 1366–69. http://dx.doi.org/10.1126/science.abc5357.

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Ultracold polyatomic molecules have potentially wide-ranging applications in quantum simulation and computation, particle physics, and quantum chemistry. For atoms and small molecules, direct laser cooling has proven to be a powerful tool for quantum science in the ultracold regime. However, the feasibility of laser-cooling larger, nonlinear polyatomic molecules has remained unknown because of their complex structure. We laser-cooled the symmetric top molecule calcium monomethoxide (CaOCH3), reducing the temperature of ~104 molecules from 22 ± 1 millikelvin to 1.8 ± 0.7 millikelvin in one dimension and state-selectively cooling two nuclear spin isomers. These results demonstrate that the use of proper ro-vibronic transitions enables laser cooling of nonlinear molecules, thereby opening a path to efficient cooling of chiral molecules and, eventually, optical tweezer arrays of complex polyatomic species.

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Yuan, Qiang, et Xi-Wen Hou. « Entropy, energy, and entanglement of localized states in bent triatomic molecules ». International Journal of Modern Physics B 31, n^o 12 (10 mai 2017) : 1750088. http://dx.doi.org/10.1142/s0217979217500886.

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The dynamics of quantum entropy, energy, and entanglement is studied for various initial states in an important spectroscopic Hamiltonian of bent triatomic molecules H2O, D2O, and H2S. The total quantum correlation is quantified in terms of the mutual information and the entanglement by the concurrence borrowed from the theory of quantum information. The Pauli entropy and the intramolecular energy usually used in the theory of molecules are calculated to establish a possible relationship between both theories. Sections of two quantities among these four quantities are introduced to visualize such relationship. Analytic and numerical simulations demonstrate that if an initial state is taken to be the stretch- or the bend-vibrationally localized state, the mutual information, the Pauli entropy, and the concurrence are dominant-positively correlated while they are dominantly anti-correlated with the interacting energy among three anharmonic vibrational modes. In particular, such correlation is more distinct for the localized state with high excitations in the bending mode. The nice quasi-periodicity of those quantities in D2O molecule reveals that this molecule prepared in the localized state in the stretching or the bending mode can be more appreciated for molecular quantum computation. However, the dynamical correlations of those quantities behave irregularly for the dislocalized states. Moreover, the hierarchy of the mutual information and the Pauli entropy is explicitly proved. Quantum entropy and energy in every vibrational mode are investigated. Thereby, the relation between bipartite and tripartite entanglements is discussed as well. Those are useful for the understanding of quantum correlations in high-dimensional states in polyatomic molecules from quantum information and intramolecular dynamics.

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Naniyil, Vineetha, Yijia Zhou, Guy Simmonds, Nathan Cooper, Weibin Li et Lucia Hackermüller. « Observation of collectivity enhanced magnetoassociation of ⁶Li in the quantum degenerate regime ». New Journal of Physics 24, n^o 11 (1 novembre 2022) : 113005. http://dx.doi.org/10.1088/1367-2630/ac9b81.

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Abstract The association process of Feshbach molecules is well described by a Landau–Zener (LZ) transition above the Fermi temperature, such that two-body physics dominates the dynamics. However, using 6Li atoms and the associated Feshbach resonance at B r = 834.1 G, we observe an enhancement of the atom–molecule coupling as the fermionic atoms reach degeneracy, demonstrating the importance of many-body coherence not captured by the conventional LZ model. In the experiment, we apply a linear association ramp ranging from adiabatic to non-equilibrium molecule association for various temperatures. We develop a theoretical model that explains the temperature dependence of the atom–molecule coupling. Furthermore, we characterize this dependence experimentally and extract the atom–molecule coupling coefficient as a function of temperature, finding qualitative agreement between our model and experimental results. In addition, we simulate the dynamics of molecular association during a nonlinear field ramp. We find that, in the non-equilibrium regime, molecular association efficiency can be enhanced by sweeping the magnetic field cubically with time. Accurate measurement of the atom–molecule coupling coefficient is important for both theoretical and experimental studies of molecular association and many-body collective dynamics.

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Abbaz, Tahar, Amel Bendjeddou et Didier Villemin. « Structural and quantum chemical studies on aryl sulfonyl piperazine derivatives ». Journal of Drug Delivery and Therapeutics 9, n^o 1-s (15 février 2019) : 88–97. http://dx.doi.org/10.22270/jddt.v9i1-s.2264.

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The optimized molecular structure and electronic features of aryl sulfonyl piperazine derivatives 1-4 have been investigated theoretically using Gaussian 09 software package and DFT/B3LYP method with 6-31G (d,p) basis set. The reactivity of the title molecules was investigated and both the positive and negative centers of the molecules were identiﬁed using molecular electrostatic potential (MEP) analysis which the results illustrate that the regions reveal the negative electrostatic potential are localized in sulfamide function while the regions presenting the positive potential are localized in the hydrogen atoms. The energies of the frontier molecular orbitals and LUMO-HOMO energy gap are measured to explain the electronic transitions. Global reactivity parameters of the aryl sulfonyl piperazine derivatives molecules were predicted to find that the more reactive and softest compound is the compound 3. Mulliken’s net charges have been calculated and results show that 3N is the more negative and 33S is the more positive charge, which Indicates extensive charge delocalization in the entire molecule. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization (π→π transitions) has been analyzed using NBO analysis. Fist hyperpolarizability is calculated in order to ﬁnd its importance in non-linear optics and the results show that the studied molecules have not the NLO applications. Keywords: sulfamide; density functional theory; computational chemistry; electronic structure; quantum chemical calculations.

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Domenikou, Natalia, Ioannis Thanopulos, Vassilios Yannopapas et Emmanuel Paspalakis. « Nonlinear Optical Rectification in a Polar Molecule-Plasmonic Nanoparticle Structure ». Materials Proceedings 4, n^o 1 (11 novembre 2020) : 8. http://dx.doi.org/10.3390/iocn2020-07873.

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The study of nonlinear optical properties of quantum systems, such as quantum dots and molecules, near plasmonic nanostructures, has attracted significant interest in the past decade. Several nonlinear phenomena have been studied in quantum systems next to plasmonic nanostructures, such as second and third harmonic generations, Kerr nonlinearity, four-wave mixing, optical bistability, and nonlinear optical rectification. The latter occurs in asymmetric quantum systems and it can be strongly influenced, enhanced, or suppressed, depending on the particular plasmonic nanostructure used. In this work, we theoretically studied the nonlinear optical rectification of a polar two-level quantum system, a specific molecule, the zinc–phalocyanine molecular complex, interacting with an optical field near a gold nanoparticle. Initially, we used the steady-state solution of the density matrix equations for determining the correct form of the nonlinear optical rectification coefficient. We then used ab initio electronic structure calculations for determining the electronic structure of the molecule under study, i.e., the necessary energy differences and the induced and permanent electric dipole moments. We also used classical electromagnetic calculations for calculating the influence of the metallic nanoparticle on the decay rates of the molecule due to the Purcell effect and on the electric field applied in the molecule in the presence of the metallic nanoparticle. We then used the above to investigate the form of the corresponding nonlinear coefficient in the absence and presence of the plasmonic nanoparticle for various parameters. We found that the nonlinear optical rectification coefficient can be enhanced for specific field polarization and for suitable distance between the molecule and the plasmonic nanoparticle. Additionally, we observed that high efficiency of this process was obtained for weak field intensity, zero pure dephasing rates, and for small values of the transition dipole moments.

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Sun, Zhong-Fa, Marc C. van Hemert, Jérôme Loreau, Ad van der Avoird, Arthur G. Suits et David H. Parker. « Molecular square dancing in CO-CO collisions ». Science 369, n^o 6501 (16 juillet 2020) : 307–9. http://dx.doi.org/10.1126/science.aan2729.

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Knowledge of rotational energy transfer (RET) involving carbon monoxide (CO) molecules is crucial for the interpretation of astrophysical data. As of now, our nearly perfect understanding of atom-molecule scattering shows that RET usually occurs by only a simple “bump” between partners. To advance molecular dynamics to the next step in complexity, we studied molecule-molecule scattering in great detail for collision between two CO molecules. Using advanced imaging methods and quasi-classical and fully quantum theory, we found that a synchronous movement can occur during CO-CO collisions, whereby a bump is followed by a move similar to a “do-si-do” in square dancing. This resulted in little angular deflection but high RET to both partners, a very unusual combination. The associated conditions suggest that this process can occur in other molecule-molecule systems.

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Gregory, Margaret, Simon Neville, Michael Schuurman et Varun Makhija. « A laboratory frame density matrix for ultrafast quantum molecular dynamics ». Journal of Chemical Physics 157, n^o 16 (28 octobre 2022) : 164301. http://dx.doi.org/10.1063/5.0109607.

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In most cases, the ultrafast dynamics of resonantly excited molecules are considered and almost always computed in the molecular frame, while experiments are carried out in the laboratory frame. Here, we provide a formalism in terms of a lab frame density matrix, which connects quantum dynamics in the molecular frame to those in the laboratory frame, providing a transparent link between computation and measurement. The formalism reveals that in any such experiment, the molecular frame dynamics vary for molecules in different orientations and that certain coherences, which are potentially experimentally accessible, are rejected by the orientation-averaged reduced vibronic density matrix. Instead, molecular angular distribution moments are introduced as a more accurate representation of experimentally accessible information. Furthermore, the formalism provides a clear definition of a molecular frame quantum tomography and specifies the requirements to perform such a measurement enabling the experimental imaging of molecular frame vibronic dynamics. Successful completion of such a measurement fully characterizes the molecular frame quantum dynamics for a molecule at any orientation in the laboratory frame.

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Solomko, Vita, Petro Kondratenko et Yuriy Lopatkin. « A Group Theoretical and Quantum Chemical Study of Electronic Absorption and Fluorescence, Vibrational Spectra, and Conformations of Trimethine Cyanine Dye Molecules ». Advances in Physical Chemistry 2016 (18 janvier 2016) : 1–7. http://dx.doi.org/10.1155/2016/6737494.

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The energetic structures and conformations of trimethine cyanine dye molecules were investigated. For research, group theoretical and quantum chemical calculation methods were used. The theoretical group analysis of electronic and vibrational structure of molecules was carried out. Also, the energetic structures and conformations of the molecule of this dye were studied. Research shows that the investigated molecule may reside in three different conformational states, one of which is highly symmetric (symmetry C2v) and the other two with low symmetry. The third conformer is characterized by lowering of binding energy of the electronic system by 0.23 eV, and the long-wavelength absorption band is shifted to lower energies. Also the group theoretical analysis of the trimethine cyanine molecule had allowed systematizing the vibrational and electronic quantum transitions and identifying the bands in the absorption spectra. It is shown that the excitation of the molecule in S1-state causes trans-cis-isomerization. The presence of the barrier of ~0.1 eV allows the fluorescence process to compete with isomerization process, but isomerization causes a decrease in the fluorescence quantum yield of the dye.

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Chatzidimitriou-Dreismann, C. Aris. « Maxwell’s Demon Observing Creation of a Molecular Vibration ». Zeitschrift für Naturforschung A 69, n^o 7 (1 juillet 2014) : 287–96. http://dx.doi.org/10.5560/zna.2014-0005.

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Quantum correlations and associated quantum information concepts (e. g. quantum discord, entanglement, quantum Maxwell’s demon) provide novel insights in various quantum-information processing tasks, quantum-thermodynamics processes, open-system dynamics, quantum molecular dynamics, and general many-body physics. We investigate a new effect of correlations accompanying collision of two quantum systems A and B, the latter being part of a larger (interacting) system B+D. In contrast to the usual case of a classical ‘environment’ or ‘demon’ (which can have only classical correlations with A+B during and after the collision), the quantum case exhibits striking new features. Here, in the frame of incoherent inelastic neutron scattering (INS) and vibrational dynamics of molecules, we report experimental evidence of a new phenomenon: quantum deficit of momentum transfer in an elementary neutron-molecule collision, in particular, in INS from single H2O molecules confined in channels with sub-nanometer diameter. The INS findings are in clear contrast to conventional theoretical expectations, but are naturally (albeit qualitative) interpreted in the frame of modern theory of quantumness of correlations, thus also proposing a new operational meaning of quantum discord and related measures.

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XUE, YONG, et G. ALI MANSOORI. « QUANTUM CONDUCTANCE AND ELECTRONIC PROPERTIES OF LOWER DIAMONDOID MOLECULES AND DERIVATIVES ». International Journal of Nanoscience 07, n^o 01 (février 2008) : 63–72. http://dx.doi.org/10.1142/s0219581x08005183.

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Diamondoids and their derivatives have found major applications as templates and as molecular building blocks in nanotechnology. An ab initio method we calculated the quantum conductance and the essential electronic properties of two lower diamondoids (adamantane and diamantane) and three of their important derivatives (amantadine, memantine and rimantadine). We also studies two artificial molecules that are built by substituting one hydrogen ion with one sodium ion in both adamantane and diamantane molecules. Most of our results are based on an infinite Au two-probe system constructed by ATK and VNL software, which comprise TRANSTA-C package. By changing various system structures and molecule orientations in linear Au and 2 × 2 Au probe systems, we found that although the conductance of adamantane and diamantane are very small, the derivatives of the lower diamondoids have considerable conductance at specific orientations and also showed interesting electronic properties. The quantum conductance of such molecules will change significantly by changing the orientations of the molecules, which approves that residues like nitrogen and sodium atoms have great effects on the conductance and electronic properties of single molecule. There are obvious peaks near Fermi energy in the transmission spectrums of artificial molecules, indicating the plateaus in I–V characteristics of such molecules.

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Tischler, Nora, Mario Krenn, Robert Fickler, Xavier Vidal, Anton Zeilinger et Gabriel Molina-Terriza. « Quantum optical rotatory dispersion ». Science Advances 2, n^o 10 (octobre 2016) : e1601306. http://dx.doi.org/10.1126/sciadv.1601306.

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The phenomenon of molecular optical activity manifests itself as the rotation of the plane of linear polarization when light passes through chiral media. Measurements of optical activity and its wavelength dependence, that is, optical rotatory dispersion, can reveal information about intricate properties of molecules, such as the three-dimensional arrangement of atoms comprising a molecule. Given a limited probe power, quantum metrology offers the possibility of outperforming classical measurements. This has particular appeal when samples may be damaged by high power, which is a potential concern for chiroptical studies. We present the first experiment in which multiwavelength polarization-entangled photon pairs are used to measure the optical activity and optical rotatory dispersion exhibited by a solution of chiral molecules. Our work paves the way for quantum-enhanced measurements of chirality, with potential applications in chemistry, biology, materials science, and the pharmaceutical industry. The scheme that we use for probing wavelength dependence not only allows one to surpass the information extracted per photon in a classical measurement but also can be used for more general differential measurements.

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JALILI, SEIFOLLAH, et FERESHTEH MORADI. « CHARGE TRANSPORT THROUGH THIOPHENE BITHIOL MOLECULE AS A MOLECULAR WIRE ». Journal of Theoretical and Computational Chemistry 04, n^o 04 (décembre 2005) : 1001–14. http://dx.doi.org/10.1142/s0219633605001945.

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The conductance properties of the thiophene bithiol molecular wire, a nano-wire connecting two metallic electrodes, were investigated using quantum-mechanical based methods such as Density Functional Theory, in conjunction with non-equilibrium Green's function formalism. Using the quantum mechanics methods, the Hamiltonians of the three main parts of system, i.e. the right lead, the device, the left lead and conductance properties of this molecular wire such as I-V curve, were calculated.

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Ungur, Liviu, Shuang-Yan Lin, Jinkui Tang et Liviu F. Chibotaru. « Single-molecule toroics in Ising-type lanthanide molecular clusters ». Chem. Soc. Rev. 43, n^o 20 (2014) : 6894–905. http://dx.doi.org/10.1039/c4cs00095a.

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Inglis, Ross, Giannis S. Papaefstathiou, Wolfgang Wernsdorfer et Euan K. Brechin. « Ferromagnetic [Mn3] Single-Molecule Magnets and Their Supramolecular Networks ». Australian Journal of Chemistry 62, n^o 9 (2009) : 1108. http://dx.doi.org/10.1071/ch09236.

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The complexes [MnIII3O(Et-sao)3(O2CPh(Cl)2)(MeOH)3(H2O)] (1), [MnIII3O(Et-sao)3(ClO4)(MeOH)3] (2), [MnIII3O(Et-sao)3(O2Ph(CF3)2)(EtOH)(H2O)3] (3), and [MnIII3O(Ph-sao)3(O2C-anthra)(MeOH)4]·Ph-saoH2 (4·Ph-saoH2) display dominant ferromagnetic exchange interactions leading to molecules with S = 6 ground states. The molecules are single molecule magnets (SMM) displaying large effective energy barriers for magnetization reversal. In each case their crystal structures reveal multiple intermolecular H-bonding interactions. Single crystal hysteresis loop measurements demonstrate that these interactions are strong enough to cause a clear field bias, but too weak to transform the spin networks into classical antiferromagnets. These three-dimensional networks of exchange coupled SMMs demonstrate that quantum tunnelling magnetization can be controlled using exchange interactions, suggesting supramolecular chemistry can be exploited to modulate the quantum physics of molecular magnets.

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Cournia, Zoe, A. C. Vaiana, G. M. Ullmann et J. C. Smith. « Derivation of a molecular mechanics force field for cholesterol ». Pure and Applied Chemistry 76, n^o 1 (1 janvier 2004) : 189–96. http://dx.doi.org/10.1351/pac200476010189.

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As a necessary step toward realistic cholesterol:biomembrane simulations, we have derived CHARMM molecular mechanics force-field parameters for cholesterol. For the parametrization we use an automated method that involves fitting the molecular mechanics potential to both vibrational frequencies and eigenvector projections derived from quantum chemical calculations. Results for another polycyclic molecule, rhodamine 6G, are also given. The usefulness of the method is thus demonstrated by the use of reference data from two molecules at different levels of theory. The frequency-matching plots for both cholesterol and rhodamine 6G show overall agreement between the CHARMM and quantum chemical normal modes, with frequency matching for both molecules within the error range found in previous benchmark studies.

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Grimaldi, Andrea, Alessandro Sergi et Antonino Messina. « Evolution of a Non-Hermitian Quantum Single-Molecule Junction at Constant Temperature ». Entropy 23, n^o 2 (25 janvier 2021) : 147. http://dx.doi.org/10.3390/e23020147.

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This work concerns the theoretical description of the quantum dynamics of molecular junctions with thermal fluctuations and probability losses. To this end, we propose a theory for describing non-Hermitian quantum systems embedded in constant-temperature environments. Along the lines discussed in [A. Sergi et al., Symmetry 10 518 (2018)], we adopt the operator-valued Wigner formulation of quantum mechanics (wherein the density matrix depends on the points of the Wigner phase space associated to the system) and derive a non-linear equation of motion. Moreover, we introduce a model for a non-Hermitian quantum single-molecule junction (nHQSMJ). In this model the leads are mapped to a tunneling two-level system, which is in turn coupled to a harmonic mode (i.e., the molecule). A decay operator acting on the two-level system describes phenomenologically probability losses. Finally, the temperature of the molecule is controlled by means of a Nosé-Hoover chain thermostat. A numerical study of the quantum dynamics of this toy model at different temperatures is reported. We find that the combined action of probability losses and thermal fluctuations assists quantum transport through the molecular junction. The possibility that the formalism here presented can be extended to treat both more quantum states (∼10) and many more classical modes or atomic particles (∼103−105) is highlighted.

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Craig, David P., et T. Thirunamachandran. « Radiation-molecule and molecule-molecule interactions. A unified viewpoint from quantum electrodynamics ». Accounts of Chemical Research 19, n^o 1 (janvier 1986) : 10–16. http://dx.doi.org/10.1021/ar00121a002.

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Roch, Nicolas, Serge Florens, Vincent Bouchiat, Wolfgang Wernsdorfer et Franck Balestro. « Quantum phase transition in a single-molecule quantum dot ». Nature 453, n^o 7195 (mai 2008) : 633–37. http://dx.doi.org/10.1038/nature06930.

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Tasakorn, M., N. Pornsuwancharoen, P. P. Yupapin et S. Thongmee. « A New Design Optical Tweezers by Triple Ring Resonator ». Advanced Materials Research 979 (juin 2014) : 504–7. http://dx.doi.org/10.4028/www.scientific.net/amr.979.504.

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We propose a new system of the multi-quantum tweezers array generation using a soliton generation control within the triple ring resonator system, whereas the dynamic tweezers can be generated within a microring device. By using the quantum processor, the entangle photon states of the tweezers can be formed, which is allowed to form the molecular quantum transmission. We have also theoretically shown that the optical tweezers can be controlled and tuned by varying the couple coefficient (κ) between 0.25 and 0.9, with ring resonator radii between 7 and 15 μm, which is available for molecule trapping. In application, the transmission of tweezers with different molecules or DNA can be performed, which is available for high density and security molecular transportation via the optical communication system.

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Qin, Yan, et Sheng-Chang Li. « Quantum phase transition of a modified spin-boson model ». Journal of Physics A : Mathematical and Theoretical 55, n^o 14 (8 mars 2022) : 145301. http://dx.doi.org/10.1088/1751-8121/ac5507.

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Abstract We adopt a modified spin-boson model to investigate the quantum phase transition in an ultracold atom-molecule conversion system involving molecule–molecule interaction. We explore the properties of ground state, entanglement entropy, and many-body dynamics, which confirm that the system exhibits a second-order phase transition from a pure atom phase to a mixed atom-molecule phase when the energy detuning is below a critical value. We obtain three scaling laws and the corresponding two critical exponents to characterize the phase transition. In particular, we discuss the effects of both the speed of ground-state dynamical evolution and the strength of molecular interaction on the phase transition. The adiabatic evolution condition is obtained as well. Our results show that the molecular interaction can greatly reduce the upper bound of the adiabatic condition, which provides a theoretical basis for easier observation of the phase transition in experiments.

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GAISIN, V. A., B. V. NOVIKOV, A. S. SOKOLOV, I. V. SHTROM, V. A. CHUGUNOV, V. G. TALALAEV, N. D. ZAKHAROV et al. « INFLUENCE OF HYDROSTATIC PRESSURE ON EXCITON PHOTOLUMINESCENCE SPECTRUM OF EXCITON MOLECULES InAs/GaAs ». International Journal of Nanoscience 06, n^o 03n04 (juin 2007) : 249–52. http://dx.doi.org/10.1142/s0219581x07004651.

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The influence of hydrostatic pressure in the range 0–12 kbar on exciton photoluminescence spectrum of InAs quantum dot molecules was studied. The molecular terms related luminescence with the increase of excitation density was obtained. For all components baric coefficients were found. Anomalies in baric dependences for p+- and d+- excited molecule states are discussed.

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Krawczuk, Anna, Daniel Pérez et Piero Macchi. « PolaBer : a program to calculate and visualize distributed atomic polarizabilities based on electron density partitioning ». Journal of Applied Crystallography 47, n^o 4 (14 juin 2014) : 1452–58. http://dx.doi.org/10.1107/s1600576714010838.

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This paper describes the program PolaBer, which calculates atomic polarizability tensors from electric field perturbations of a partitioned electron density distribution. Among many possible partitioning schemes, PolaBer is currently using the quantum theory of atoms in molecules and it is interfaced to programs that apply such a partitioning. The calculation of the atomic tensors follows the idea suggested by Keith [The Quantum Theory of Atoms in Molecules: From Solid State to DNA and Drug Design, (2007), edited by C. F. Matta & R. J. Boyd. Weinheim: Wiley-VCH], which enables the removal of the intrinsic origin dependence of the atomic charge contributions to the molecular dipole moment. This scheme allows the export, within chemically equivalent functional groups, of properties calculated from atomic dipoles, such as for example the atomic polarizabilities. The software permits visualization of the tensors and calculation of straightforward optical properties of a molecule (like the molar refractive index) or a crystal (assuming the molecule in a given crystal lattice).

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Christou, George, Dante Gatteschi, David N. Hendrickson et Roberta Sessoli. « Single-Molecule Magnets ». MRS Bulletin 25, n^o 11 (novembre 2000) : 66–71. http://dx.doi.org/10.1557/mrs2000.226.

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Magnets are widely used in a large number of applications, and their market is larger than that of semiconductors. Information storage is certainly one of the most important uses of magnets, and the lower limit to the size of the memory elements is provided by the superparamagnetic size, below which information cannot be permanently stored because the magnetization freely fluctuates. This occurs at room temperature for particles in the range of 10–100 nm, owing to the nature of the material. However, even smaller particles can in principle be used either by working at lower temperatures or by taking advantage of the onset of quantum size effects, which can make nanomagnets candidates for the construction of quantum computers.

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MATSUI, A. H., M. TAKESHIMA, K. MIZUNO et T. AOKI-MATSUMOTO. « PHOTOPHYSICAL OVERVIEW OF EXCITATION ENERGY TRANSFER IN ORGANIC MOLECULAR ASSEMBLIES — A ROUTE TO STUDY BIO-MOLECULAR ARRAYS — ». International Journal of Modern Physics B 15, n^o 28n30 (10 décembre 2001) : 3857–60. http://dx.doi.org/10.1142/s0217979201008846.

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Excitonic processes in organic molecular crystals are discussed in terms of two parameters, the crystal size and the constituent molecule size. From the luminescence and absorption spectra of a series of aromatic molecular crystals we find a systematic change in exciton energy transport as functions of the size of crystal and its constituent molecule size. Characteristic features of bulk crystals and microcrystallites are as follows. (1) In bulk crystals exciton energy transport depends on the constituent molecule size. When molecules are small, the exciton energy transport occurs by free excitons, but when molecules are large free exciton transport disappears because excitons get self-trapped. (2) In microcrystallites, exciton energy transport depends on the crystallite size. When the size is larger than a critical one, excitons travel as quantum mechanical waves but when the size is smaller than the critical one the exciton waves get confined within the crystallite. The results are independent of the chemical species of constituent molecules and thus applicable to novel molecular arrays such as biological molecular arrays.

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Takaloo, Ashkan Vakilipour, et Hatef Sadeghi. « Quantum Interference Enhanced Thermoelectricity in Ferrocene Based Molecular Junctions ». Journal of Nanoscience and Nanotechnology 19, n^o 11 (1 novembre 2019) : 7452–55. http://dx.doi.org/10.1166/jnn.2019.16622.

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Recent experimental indications of room-temperature quantum interference in the sub-nanometer single molecules suggest that such effects could be utilized to engineer thermoelectric properties of organic single molecule junctions. In this paper, we show that the thermoelectric power factor is significantly enhanced in double path ferrocene cycles compared to the single path counterpart. Due to quantum interference in the double path structure, the Seebeck coefficient is significantly enhanced while the conductance is less affected compared to single path structure. The power factor of the ferrocene cycles are 1–2 orders of magnitude higher than the best organic material reported today. This opens new avenues for future molecular scale organometallic thermoelectricity.

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MAITI, SANTANU K. « QUANTUM TRANSPORT THROUGH SINGLE PHENALENYL MOLECULE : EFFECT OF INTERFACE STRUCTURE ». International Journal of Nanoscience 06, n^o 06 (décembre 2007) : 415–22. http://dx.doi.org/10.1142/s0219581x07004985.

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The electronic transport characteristics through a single phenalenyl molecule sandwiched between two metallic electrodes are investigated by using Green's function technique. A parametric approach, based on the tight-binding model, is used to study the transport characteristics through such molecular bridge system. The electronic transport properties are significantly influenced by (a) the molecule-to-electrodes interface structure and (b) the molecule-to-electrodes coupling strength.

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