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1
Filatov, Aleksandr Nikolaevich, and Vladimir Kuz'mich Shilov. "Radial dynamics of electrons in two-section linear accelerator." International Journal of Electrical and Computer Engineering (IJECE) 9, no. 1 (February 1, 2019): 215. http://dx.doi.org/10.11591/ijece.v9i1.pp215-220.
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This article discusses possibility of harness wiring with the use of focusing system of high frequency eigenfields of accelerating resonators in standing wave linear accelerators on the basis of biperiodic slowing systems. The scopes of business activities and specificity of existing engineering processes applied in industry, especially in chemistry and metallurgy, require for special measures on environmental protection. At present electron linear accelerators operating in pulse mode are used for application purposes. Such accelerators can be characterized by sufficient beam power for efficient industrial use and for environmental protection. The results of numerical analysis of electron dynamics in two-section accelerator upon various initial conditions are presented. The obtained results are applied for development of actual accelerator, calculated and experimental data are given. The performed experimental study confirmed possibility of development of standing wave linear accelerator without external magnetic focusing system with output beam diameter of not higher than . The results of calculations of beam dynamics are experimentally verified.
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Quintas-Sánchez, Ernesto, and Richard Dawes. "Spectroscopy and Scattering Studies Using Interpolated Ab Initio Potentials." Annual Review of Physical Chemistry 72, no. 1 (April 20, 2021): 399–421. http://dx.doi.org/10.1146/annurev-physchem-090519-051837.
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The Born–Oppenheimer potential energy surface (PES) has come a long way since its introduction in the 1920s, both conceptually and in predictive power for practical applications. Nevertheless, nearly 100 years later—despite astonishing advances in computational power—the state-of-the-art first-principles prediction of observables related to spectroscopy and scattering dynamics is surprisingly limited. For example, the water dimer, (H2O)2, with only six nuclei and 20 electrons, still presents a formidable challenge for full-dimensional variational calculations of bound states and is considered out of reach for rigorous scattering calculations. The extremely poor scaling of the most rigorous quantum methods is fundamental; however, recent progress in development of approximate methodologies has opened the door to fairly routine high-quality predictions, unthinkable 20 years ago. In this review, in relation to the workflow of spectroscopy and/or scattering studies, we summarize progress and challenges in the component areas of electronic structure calculations, PES fitting, and quantum dynamical calculations.
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TO, TRAN THINH, and STEFAN ADAMS. "CHARGE TRANSPORT AND LIGHT ABSORPTION IN CONJUGATED SYSTEMS FROM EXTENDED HÜCKEL METHOD AND MARCUS THEORY." International Journal of Computational Materials Science and Engineering 01, no. 02 (June 2012): 1250020. http://dx.doi.org/10.1142/s2047684112500200.
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A simple first principle model was developed based on extended Hückel-type orbital calculation, Marcus electron transport theory and two-dimensional-electron-gas model for the treatment of charge transport in conjugated polymers. Though simple and easy to compute, the effect of the applied electric-field is factored in. Based on this, a complete one-dimensional device model with a single layer of conjugated polymer sandwiched between two electrodes was developed with poly(3-hexylthiophene) (P3HT) as a case study. Simulated J-V curves show that π-π charge transport is much more pronounced than intra-chain transport, hence agree with previous findings. Using the same framework, we also calculated the absorption spectra of P3HT by considering the electronic energy barrier for electronic transitions that would satisfy Franck–Condon principle. Absorption spectra closely harmonize to experimental UV-Vis result. The model also reveals intra-chain electronic transitions to be the dominant absorption mechanism. All parameters of the model are obtained from either ab-initio Density Functional Theory (DFT) or Molecular Dynamics (MD) calculations, so that this model is capable of predicting charge transport and light absorption properties of new conjugated polymers without introducing fit parameters.
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Segatta, Francesco, David M. Rogers, Naomi T. Dyer, Ellen E. Guest, Zhuo Li, Hainam Do, Artur Nenov, Marco Garavelli, and Jonathan D. Hirst. "Near-Ultraviolet Circular Dichroism and Two-Dimensional Spectroscopy of Polypeptides." Molecules 26, no. 2 (January 13, 2021): 396. http://dx.doi.org/10.3390/molecules26020396.
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A fully quantitative theory of the relationship between protein conformation and optical spectroscopy would facilitate deeper insights into biophysical and simulation studies of protein dynamics and folding. In contrast to intense bands in the far-ultraviolet, near-UV bands are much weaker and have been challenging to compute theoretically. We report some advances in the accuracy of calculations in the near-UV, which were realised through the consideration of the vibrational structure of the electronic transitions of aromatic side chains.
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Zhu, Zhengyang, Kai Ren, Huabing Shu, Zhen Cui, Zhaoming Huang, Jin Yu, and Yujing Xu. "First-Principles Study of Electronic and Optical Properties of Two-Dimensional WSSe/BSe van der Waals Heterostructure with High Solar-to-Hydrogen Efficiency." Catalysts 11, no. 8 (August 18, 2021): 991. http://dx.doi.org/10.3390/catal11080991.
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In this paper, the optical and electronic properties of WSSe/BSe heterostructure are investigated by first-principles calculations. The most stable stacking pattern of the WSSe/BSe compounds is formed by van der Waals interaction with a thermal stability proved by ab initio molecular dynamics simulation. The WSSe/BSe heterostructure exhibits a type-I band alignment with direct bandgap of 2.151 eV, which can improve the effective recombination of photoexcited holes and electrons. Furthermore, the band alignment of the WSSe/BSe heterostructure can straddle the water redox potential at pH 0–8, and it has a wide absorption range for visible light. In particular, the solar-to-hydrogen efficiency of the WSSe/BSe heterostructure is obtained at as high as 44.9% at pH 4 and 5. All these investigations show that the WSSe/BSe heterostructure has potential application in photocatalysts to decompose water.
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Autreto, P. A., J. M. de Sousa, and D. S. Galvao. "On the Dynamics of Graphdiyne Hydrogenation." MRS Proceedings 1549 (2013): 59–64. http://dx.doi.org/10.1557/opl.2013.608.
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ABSTRACTGraphene is a two-dimensional (2D) hexagonal array of carbon atoms in sp2-hybridized states. Graphene presents unique and exceptional electronic, thermal and mechanical properties. However, in its pristine state graphene is a gapless semiconductor, which poses some limitations to its use in some transistor electronics. Because of this there is a renewed interest in other possible two-dimensional carbon-based structures similar to graphene. Examples of this are graphynes and graphdiynes, which are two-dimensional structures, composed of carbon atoms in sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two acetylenic groups) were recently synthesized and they can be intrinsically nonzero gap systems. These systems can be easily hydrogenated and the amount of hydrogenation can be used to tune the band gap value. In this work we have investigated, through fully atomistic molecular dynamics simulations with reactive force field (ReaxFF), the structural and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes. Our results showed that depending on whether the atoms are in the benzenoid rings or as part of the acetylenic groups, the rates of hydrogenation are quite distinct and change in time in a very complex pattern. Initially, the most probable sites to be hydrogenated are the carbon atoms forming the triple bonds, as expected. But as the amount of hydrogenation increases in time this changes and then the carbon atoms forming single bonds become the preferential sites. The formation of correlated domains observed in hydrogenated graphene is no longer observed in the case of graphdiynes. We have also carried out ab initio DFT calculations for model structures in order to test the reliability of ReaxFF calculations.
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Pham, Thang, Sehoon Oh, Patrick Stetz, Seita Onishi, Christian Kisielowski, Marvin L. Cohen, and Alex Zettl. "Torsional instability in the single-chain limit of a transition metal trichalcogenide." Science 361, no. 6399 (July 19, 2018): 263–66. http://dx.doi.org/10.1126/science.aat4749.
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The scientific bounty resulting from the successful isolation of few to single layers of two-dimensional materials suggests that related new physics resides in the few- to single-chain limit of one-dimensional materials. We report the synthesis of the quasi–one-dimensional transition metal trichalcogenide NbSe3 (niobium triselenide) in the few-chain limit, including the realization of isolated single chains. The chains are encapsulated in protective boron nitride or carbon nanotube sheaths to prevent oxidation and to facilitate characterization. Transmission electron microscopy reveals static and dynamic structural torsional waves not found in bulk NbSe3 crystals. Electronic structure calculations indicate that charge transfer drives the torsional wave instability. Very little covalent bonding is found between the chains and the nanotube sheath, leading to relatively unhindered longitudinal and torsional dynamics for the encapsulated chains.
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Guskov, Vladislav, Fabian Langkabel, Matthias Berg, and Annika Bande. "An Impurity Effect for the Rates of the Interparticle Coulombic Decay." Quarks: Brazilian Electronic Journal of Physics, Chemistry and Materials Science 3, no. 1 (November 28, 2020): 17–30. http://dx.doi.org/10.34019/2674-9688.2020.v3.31928.
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The interparticle Coulombic decay is a synchronized decay and ionization phenomenon occurring on two separated and only Coulomb interaction coupled electron binding sites. This publication explores how drastically small environmental changes in between the two sites, basically impurities, can alter the ionization properties and process rate, although the involved electronic transitions remain unaltered. A comparison among the present electron dynamics calculations for the example of different types of quantum dots, accommodating a one- or a two-dimensional continuum for the outgoing electron, and the well-investigated atomic and molecular cases with three-dimensional continuum, reveals that the impurity effect is most pronounced the stronger that electron is confined. This necessarily leads to challenges and opportunities in a quantum dot experiment to prove the interparticle Coulombic decay.
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Cao, Bin, Ji-Wei Dong, and Ming-He Chi. "Electrical Breakdown Mechanism of Transformer Oil with Water Impurity: Molecular Dynamics Simulations and First-Principles Calculations." Crystals 11, no. 2 (January 27, 2021): 123. http://dx.doi.org/10.3390/cryst11020123.
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Water impurity is the essential factor of reducing the insulation performance of transformer oil, which directly determines the operating safety and life of a transformer. Molecular dynamics simulations and first-principles electronic-structure calculations are employed to study the diffusion behavior of water molecules and the electrical breakdown mechanism of transformer oil containing water impurities. The molecular dynamics of an oil-water micro-system model demonstrates that the increase of aging acid concentration will exponentially expedite thermal diffusion of water molecules. Density of states (DOS) for a local region model of transformer oil containing water molecules indicates that water molecules can introduce unoccupied localized electron-states with energy levels close to the conduction band minimum of transformer oil, which makes water molecules capable of capturing electrons and transforming them into water ions during thermal diffusion. Subsequently, under a high electric field, water ions collide and impact on oil molecules to break the molecular chain of transformer oil, engendering carbonized components that introduce a conduction electronic-band in the band-gap of oil molecules as a manifestation of forming a conductive region in transformer oil. The conduction channel composed of carbonized components will be eventually formed, connecting two electrodes, with the carbonized components developing rapidly under the impact of water ions, based on which a large number of electron carriers will be produced similar to “avalanche” discharge, leading to an electrical breakdown of transformer oil insulation. The water impurity in oil, as the key factor for forming the carbonized conducting channel, initiates the electric breakdown process of transformer oil, which is dominated by thermal diffusion of water molecules. The increase of aging acid concentration will significantly promote the thermal diffusion of water impurities and the formation of an initial conducting channel, accounting for the degradation in dielectric strength of insulating oil containing water impurities after long-term operation of the transformer.
10
Katsavrias, C., I. A. Daglis, W. Li, S. Dimitrakoudis, M. Georgiou, D. L. Turner, and C. Papadimitriou. "Combined effects of concurrent Pc5 and chorus waves on relativistic electron dynamics." Annales Geophysicae 33, no. 9 (September 25, 2015): 1173–81. http://dx.doi.org/10.5194/angeo-33-1173-2015.
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Abstract. We present electron phase space density (PSD) calculations as well as concurrent Pc5 and chorus wave activity observations during two intense geomagnetic storms caused by interplanetary coronal mass ejections (ICMEs) resulting in contradicting net effect. We show that, during the 17 March 2013 storm, the coincident observation of chorus and relativistic electron enhancements suggests that the prolonged chorus wave activity seems to be responsible for the enhancement of the electron population in the outer radiation belt even in the presence of pronounced outward diffusion. On the other hand, the significant depletion of electrons, during the 12 September 2014 storm, coincides with long-lasting outward diffusion driven by the continuous enhanced Pc5 activity since chorus wave activity was limited both in space and time.
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Khan, Muhammad Yar, Yan Liu, Tao Wang, Hu Long, Miaogen Chen, and Dawei Gao. "A First-Principle Study of Monolayer Transition Metal Carbon Trichalcogenides." Journal of Superconductivity and Novel Magnetism 34, no. 8 (July 27, 2021): 2141–49. http://dx.doi.org/10.1007/s10948-021-05980-1.
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AbstractMonolayer MnCX3 metal–carbon trichalcogenides have been investigated by using the first-principle calculations. The compounds show half-metallic ferromagnetic characters. Our results reveal that their electronic and magnetic properties can be altered by applying uniaxial or biaxial strain. By tuning the strength of the external strain, the electronic bandgap and magnetic ordering of the compounds change and result in a phase transition from the half-metallic to the semiconducting phase. Furthermore, the vibrational and thermodynamic stability of the two-dimensional structure has been verified by calculating the phonon dispersion and molecular dynamics. Our study paves guidance for the potential applications of these two mono-layers in the future for spintronics and straintronics devices.
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Zhai, Dawei, and Nancy Sandler. "Electron dynamics in strained graphene." Modern Physics Letters B 33, no. 28 (October 10, 2019): 1930001. http://dx.doi.org/10.1142/s0217984919300011.
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This paper presents a theoretical description of the effects of strain induced by out-of-plane deformations on charge distributions and transport on graphene. A review of a continuum model for electrons using the Dirac formalism is complemented with elasticity theory to represent strain fields. The resulting model is cast in terms of scalar and pseudo-magnetic fields that control electron dynamics. Two distinct geometries, a bubble and a fold, are chosen to represent the most commonly observed deformations in experimental settings. It is shown that local charge accumulation regions appear in deformed areas, with a peculiar charge distribution that favors occupation of one sublattice only. This unique phenomenon that allows to distinguish each carbon atom in the unit cell, is the manifestation of a sublattice symmetry broken phase. For specific parameters, resonant states appear in localized charged regions, as shown by the emergence of discrete levels in band structure calculations. These findings are presented in terms of intuitive pictures that exploit analogies with confinement produced by square barriers. In addition, electron currents through strained regions are spatially separated into their valley components, making possible the manipulation of electrons with different valley indices. The degree of valley filtering (or polarization) for a specific system can be controlled by properly designing the strained area. The comparison between efficiencies of filters built with this type of geometries identifies extended deformations as better valley filters. A proposal for their experimental implementations as component of devices, and a discussion for potential observation of novel physics in strained structures are presented at the end of the paper.
13
Canton, S. E., X. Zhang, Y. Liu, J. Zhang, M. Pápai, A. Corani, A. L. Smeigh, et al. "Watching the dynamics of electrons and atoms at work in solar energy conversion." Faraday Discussions 185 (2015): 51–68. http://dx.doi.org/10.1039/c5fd00084j.
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The photochemical reactions performed by transition metal complexes have been proposed as viable routes towards solar energy conversion and storage into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process on the atomic scale. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium–cobalt dyads, which belong to the large family of donor–bridge–acceptor systems. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the two metal centers are monitored. These experiments show that the nature of the connecting bridge is decisive for controlling the forward and the backward electron transfer rates, a result supported by quantum chemistry calculations. More generally, this work illustrates how ultrafast optical and X-ray techniques can disentangle the influence of spin, electronic and nuclear factors on the intramolecular electron transfer process. Finally, some implications for further improving the design of bridged sensitizer-catalysts utilizing the presented methodology are outlined.
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DAHLEN, NILS ERIK. "EFFECT OF ELECTRON CORRELATION ON THE TWO-PARTICLE DYNAMICS OF A HELIUM ATOM IN A STRONG LASER PULSE." International Journal of Modern Physics B 16, no. 03 (January 30, 2002): 415–52. http://dx.doi.org/10.1142/s0217979202007987.
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This review discusses the complicated two-electron dynamics of a helium atom in an intense, short laser pulse. A helium gas in femtosecond laser pulses at long wave lengths (λ~700 nm) and high intensities (I~1015 W /cm2) produces surprisingly high numbers of He2+ ions. These laser fields cause large and fast electron oscillations, which makes a solution of the time-dependent Schrödinger equation numerically demanding. The system can be studied using a one-dimensional model atom, which has many of the same properties as the He atom. Using the one-dimensional model, the importance of including electron correlation in a simplified description of the two-electron dynamics is demonstrated. It is shown that electron correlation becomes much less important if the laser field has a short wave length, in which case the electron oscillations are smaller and slower. The problem of including electron correlation in the calculations is discussed in terms of approaches such as time-dependent Hartree–Fock, time-dependent density functional theory and time-dependent extended Hartree–Fock. Some of the commonly used semi-classical models for describing the double-ionization process are presented.
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Zhao, Bin, Shanyu Han, Christopher L. Malbon, Uwe Manthe, David R. Yarkony, and Hua Guo. "Full-dimensional quantum stereodynamics of the non-adiabatic quenching of OH(A2Σ+) by H2." Nature Chemistry 13, no. 9 (August 9, 2021): 909–15. http://dx.doi.org/10.1038/s41557-021-00730-1.
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AbstractThe Born–Oppenheimer approximation, assuming separable nuclear and electronic motion, is widely adopted for characterizing chemical reactions in a single electronic state. However, the breakdown of the Born–Oppenheimer approximation is omnipresent in chemistry, and a detailed understanding of the non-adiabatic dynamics is still incomplete. Here we investigate the non-adiabatic quenching of electronically excited OH(A2Σ+) molecules by H2 molecules using full-dimensional quantum dynamics calculations for zero total nuclear angular momentum using a high-quality diabatic-potential-energy matrix. Good agreement with experimental observations is found for the OH(X2Π) ro-vibrational distribution, and the non-adiabatic dynamics are shown to be controlled by stereodynamics, namely the relative orientation of the two reactants. The uncovering of a major (in)elastic channel, neglected in a previous analysis but confirmed by a recent experiment, resolves a long-standing experiment–theory disagreement concerning the branching ratio of the two electronic quenching channels.
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LEBO, I. G., N. N. DEMCHENKO, A. B. ISKAKOV, J. LIMPOUCH, V. B. ROZANOV, and V. F. TISHKIN. "Simulation of high-intensity laser–plasma interactions by use of the 2D Lagrangian code “ATLANT-HE”." Laser and Particle Beams 22, no. 3 (July 2004): 267–73. http://dx.doi.org/10.1017/s0263034604223096.
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Hot electrons may significantly influence interaction of ultrashort laser pulses with solids. Accurate consideration of resonant absorption of laser energy and hot electron generation at a critical surface was achieved through the developed physical and mathematical models. A two-dimensional (2D) ray-tracing algorithm has been developed to simulate laser beam refraction and Bremsstrahlung absorption with allowance for nonlinear influence of a strong electromagnetic field. Hot electron transport was considered as a straight-line flow weakening by a friction force calculated in the approximation of the average state of ionization. Developed models were coupled with the 2D Lagrangian gas dynamic code “ATLANT” that takes into account nonlinear heat transport. The developed program has been applied to simulate irradiation of Al foils by picosecond laser double pulses. Hot electron transport and heating resulted in thin foil explosions. The transition from the exploding foil regime to the ablative one with foil thickening has been simulated and analyzed at various values of laser light intensity. In second series of calculations we have modeled the interaction of a nanosecond iodine laser with a two-layered target.
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Kurzyna, Marcin, and Tomasz Kwapiński. "Electron Pumping and Spectral Density Dynamics in Energy-Gapped Topological Chains." Applied Sciences 11, no. 2 (January 15, 2021): 772. http://dx.doi.org/10.3390/app11020772.
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Electron pumping through energy-gapped systems is restricted for vanishing local density of states at the Fermi level. In this paper, we propose a topological Su–Schrieffer–Heeger (SSH) chain between unbiased leads as an effective electron pump. We analyze the electron transport properties of topologically trivial and nontrivial systems in the presence of external time-dependent forces in the form of one-Gaussian or two-Gaussian perturbations (train impulses). We have found that the topologically trivial chain stands for much better charge pump than other normal or nontrivial chains. It is important that, during the perturbation, electrons are pumped through the mid-gap temporary states or through the induced sidebands states outside the energy gap. We also analyze the local density of states dynamics during the quench transition between different topological phases of the SSH chain. It turns out that after the quench, the edge topological states migrate through other sites and can temporarily exist in a topologically trivial part of the system. The tight-binding Hamiltonian and the evolution operator technique are used in our calculations.
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Deng, Gang-Hua, Yuqin Qian, Tong Zhang, Jian Han, Hanning Chen, and Yi Rao. "Two-dimensional electronic–vibrational sum frequency spectroscopy for interactions of electronic and nuclear motions at interfaces." Proceedings of the National Academy of Sciences 118, no. 34 (August 20, 2021): e2100608118. http://dx.doi.org/10.1073/pnas.2100608118.
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Interactions of electronic and vibrational degrees of freedom are essential for understanding excited-states relaxation pathways of molecular systems at interfaces and surfaces. Here, we present the development of interface-specific two-dimensional electronic–vibrational sum frequency generation (2D-EVSFG) spectroscopy for electronic–vibrational couplings for excited states at interfaces and surfaces. We demonstrate this 2D-EVSFG technique by investigating photoexcited interface-active (E)-4-((4-(dihexylamino) phenyl)diazinyl)-1-methylpyridin-1- lum (AP3) molecules at the air–water interface as an example. Our 2D-EVSFG experiments show strong vibronic couplings of interfacial AP3 molecules upon photoexcitation and subsequent relaxation of a locally excited (LE) state. Time-dependent 2D-EVSFG experiments indicate that the relaxation of the LE state, S2, is strongly coupled with two high-frequency modes of 1,529.1 and 1,568.1 cm−1. Quantum chemistry calculations further verify that the strong vibronic couplings of the two vibrations promote the transition from the S2 state to the lower excited state S1. We believe that this development of 2D-EVSFG opens up an avenue of understanding excited-state dynamics related to interfaces and surfaces.
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García-López, Cristian Eduardo, Irineo-Pedro Zaragoza Rivera, Benjamín Vargas-Arista, and Verónica Estrella-Suarez. "Molecular Structures of ZnO by Aggregates of Atoms and Interaction of Two Monolayers." European Journal of Engineering Research and Science 4, no. 10 (October 30, 2019): 162–66. http://dx.doi.org/10.24018/ejers.2019.4.10.1605.
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The first-principles calculations are useful for determining electronic and structural properties for a model that simulates a material composed of atomic clusters of ZnO through the analysis of interaction energies and charge distribution. The two-dimensional structural form of ZnO aggregates shows regularly flat hexagons obtained in models of 6, 27 and 54 atoms of Zinc and Oxygen. The structure of a three-dimensional system was determined by dynamics calculations by using the interaction of a pair of monolayers consisting of 108 atoms and as a result, a cage structure was formed from a cluster of Zn54 and O54 identifying only bond atoms at the ends that promote the union of monolayers. The stable structure shows modifications of the atomic bonds in whose centers hexagonal rings prevailed and at the arrangements of the end of triangles, squares, pentagons and even rings of 10 and 11 atoms were obtained. Atomic positions and charge distribution were analyzed based on the methodology used Density Functional Theory (DFT), with the becke88-LYP exchange and correlation functional.
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Förner, Wolfgang. "Theoretical Study of Bipolaron Dynamics in Polyparaphenylene: II. Density Functional Theory (DFT) Calculations on Neutral Dimers and Semiempirical Hückel-Type Calculations on Neutral and Charged Model Chains." Collection of Czechoslovak Chemical Communications 70, no. 6 (2005): 689–730. http://dx.doi.org/10.1135/cccc20050689.
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We have derived earlier the rather lengthy formalism for time simulations in poly(p-phenylene), treating the rings as semirigid rotors. To this end the Euler-Lagrange formalism had to be used. As a first step we intended to parametrize the simplified Hückel-type hamiltonian on the basis of density functional theory (DFT) calculations on some dimeric model systems. The results of this attempt are reported here. However, calculations on much longer chains, containing up to 200 rings, show a clear tendency of our model to favor the quinoid B-phase structure over the aromatic one. Further, in doubly charged chains, the charge tends to remain unseparated and to be completely delocalized over virtually the complete part of the chain, that is in B-phase conformation. The bipolaron width turns out to be extremely small, of about 10 rings in a chain having 200 rings. This is rather unexpected and interpreted as a shortcoming of the Hückel-type nature of the hamiltonian. The reason is that in the Hückel-type model the two electrons, taken away to charge the chain, are from the same orbital, and thus charge separation is more difficult, leading, in this case, only to a delocalization, keeping the bipolaron small. We assume, that in line with Prof. Paldus' work, the inclusion of direct electron-electron interactions in the form of a Pariser-Parr-Pople (PPP) type model could overcome this difficulty. The treatment has to be done, probably, in an open shell form to make possible spin separation, if necessary. Care has to be taken for spin contaminations in such treatments and possibly even the explicit inclusion of electron correlation might be necessary. In this paper we report our model which was derived in detail in a previous paper. Then we discuss the parametrization attempts and our results on longer chains. In conclusion our suggestion is that a PPP type model must be used at least to allow for bipolaron calculations and confinement of the two like charges. Such calculations would be the content of a forthcoming paper.
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Paul, Bishwajit, Tanmoy Banerjee, and B. C. Sarkar. "Spatiotemporal Dynamics of a Network of Coupled Time-Delay Digital Tanlock Loops." International Journal of Bifurcation and Chaos 26, no. 05 (May 2016): 1650076. http://dx.doi.org/10.1142/s0218127416500760.
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The time-delay digital tanlock loop (TDTLs) is an important class of phase-locked loop that is widely used in electronic communication systems. Although nonlinear dynamics of an isolated TDTL has been studied in the past but the collective behavior of TDTLs in a network is an important topic of research and deserves special attention as in practical communication systems separate entities are rarely isolated. In this paper, we carry out the detailed analysis and numerical simulations to explore the spatiotemporal dynamics of a network of a one-dimensional ring of coupled TDTLs with nearest neighbor coupling. The equation representing the network is derived and we carry out analytical calculations using the circulant matrix formalism to obtain the stability criteria. An extensive numerical simulation reveals that with the variation of gain parameter and coupling strength the network shows a variety of spatiotemporal dynamics such as frozen random pattern, pattern selection, spatiotemporal intermittency and fully developed spatiotemporal chaos. We map the distinct dynamical regions of the system in two-parameter space. Finally, we quantify the spatiotemporal dynamics by using quantitative measures like Lyapunov exponent and the average quadratic deviation of the full network.
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Sadlej, Andrzej J., Ota Bludský, and Vladimír Špirko. "Vibrational Dynamics of the H2O . HF Complex. Potential Energy and Electric Dipole Moment Surfaces." Collection of Czechoslovak Chemical Communications 58, no. 12 (1993): 2813–30. http://dx.doi.org/10.1135/cccc19932813.
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A total of 330 points on the potential energy and electric dipole moment surfaces of the ground electronic state of the H2O . HF complex have been calculated ab initio using the SCF method and many-body perturbation theory (MBPT). To keep the calculations manageable, the geometry parameters of H2O were fixed at their experimental values and only certain two dimensional sections of the total surfaces have been evaluated. for each of the two-dimensional surface section, analytic potential energy and electric dipole moment functions have been fitted through the points and corresponding vibrational energy levels and effective electric dipole moments have been calculated using approximate vibrational Hamiltonians. The calculated values of resulting vibrational energies and effective electric dipoles from differently wide intervals for different vibrational modes. The intervals corresponding to the most interesting low frequency modes (out-of-plane and H2O vs HF stretching) are very narrow and coincide satisfactory with the corresponding experimental values. A very reasonable agreement has also been obtained for the equilibrium geometry, electric dipole moment and dissociation energy De of the complex. These findings lead us to believe that the calculated potential energy and electric dipole moment surfaces are sufficiently accurate for predicting purposes and rationalization of the so far unassigned spectral data of H2O . HF.
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Lee, Gun-Do, Alex W. Robertson, Sungwoo Lee, Yung-Chang Lin, Jeong-Wook Oh, Hwanyeol Park, Young-Chang Joo, et al. "Direct observation and catalytic role of mediator atom in 2D materials." Science Advances 6, no. 24 (June 2020): eaba4942. http://dx.doi.org/10.1126/sciadv.aba4942.
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The structural transformations of graphene defects have been extensively researched through aberration-corrected transmission electron microscopy (AC-TEM) and theoretical calculations. For a long time, a core concept in understanding the structural evolution of graphene defects has been the Stone-Thrower-Wales (STW)–type bond rotation. In this study, we show that undercoordinated atoms induce bond formation and breaking, with much lower energy barriers than the STW-type bond rotation. We refer to them as mediator atoms due to their mediating role in the breaking and forming of bonds. Here, we report the direct observation of mediator atoms in graphene defect structures using AC-TEM and annular dark-field scanning TEM (ADF-STEM) and explain their catalytic role by tight-binding molecular dynamics (TBMD) simulations and image simulations based on density functional theory (DFT) calculations. The study of mediator atoms will pave a new way for understanding not only defect transformation but also the growth mechanisms in two-dimensional materials.
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LUKEŠ, VLADIMÍR, ROLAND ŠOLC, MARIO BARBATTI, HANS LISCHKA, and HARALD-FRIEDRICH KAUFFMANN. "TORSIONAL POTENTIALS AND FULL-DIMENSIONAL SIMULATION OF ELECTRONIC ABSORPTION SPECTRA OF para-PHENYLENEVINYLENE OLIGOMERS USING SEMIEMPIRICAL HAMILTONIANS." Journal of Theoretical and Computational Chemistry 09, no. 01 (February 2010): 249–63. http://dx.doi.org/10.1142/s0219633610005645.
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A systematic study of torsional potential curves in electronic ground state based on second-order Møller–Plesset energy (MP2), density functional theory (DFT), and Austin mode 1 (AM1) methods is presented for para-phenylenevinylene oligomers constructed from two to four aromatic rings. The semiempirical AM1 approach gives the correct location of potential energy minima in comparison with the reference MP2 calculations and literature data. However, the semiempirical AM1 energy barriers at perpendicular orientation are ca. 30% smaller than the MP2 ones. The DFT calculations indicate optimal planar structures and the barriers are three times higher than MP2 values. Excited-state potential energy curves evaluated from vertical excitations at the time-dependent density functional theory (TD-DFT) and ab initio CI levels exhibit much steeper increase of values in the vicinity of perpendicular orientation than in the semiempirical Zerner's intermediate neglect of differential overlap (ZINDO) and ab initio RI-CC2 cases. The effects of vibrational motion of phenylene rings on the torsional broadening of absorption spectra were estimated from semi-classical molecular dynamics simulations and harmonic oscillator sampling. The simulated spectra agree well with the experiment and allow estimating the conformer distribution of the molecules.
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Erkoc, Sakir. "Cluster, Surface and Bulk Properties of ZnCd Binary Alloys: Molecular-Dynamics Simulations." Materials Science Forum 502 (December 2005): 51–56. http://dx.doi.org/10.4028/www.scientific.net/msf.502.51.
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The structural and electronic properties of isolated neutral ZnmCdn clusters for m+n £ 3 have been investigated by performing density functional theory calculations at B3LYP level. The optimum geometries, vibrational frequencies, electronic structures, and the possible dissosiation channels of the clusters considered have been obtained. An empirical many-body potential energy function (PEF), which comprices two- and three-body atomic interactions, has been developed to investigate the structural features and energetics of ZnmCdn (m+n=3,4) microclusters. The most stable structures were found to be triangular for the three-atom clusters and tetrahedral for the four-atom clusters. On the other hand, the structural features and energetics of Znn-mCdm (n=7,8) microclusters, and Zn50, Cd50, Zn25Cd25, Zn12Cd38, and Zn38Cd12 nanoparticles have been investigated by performing molecular-dynamics computer simulations using the developed PEF. The most stable structures were found to be compact and three-dimensional for all elemental and mixed clusters. An interesting structural feature of the mixed clusters is that Zn and Cd atoms do not mix in mixed clusters, they come together almost without mixing. Surface and bulk properties of Zn, Cd, and ZnCd systems have been investigated too by performing molecular-dynamics simulations using the developed PEF. Surface reconstruction and multilayer relaxation on clean surfaces, adatom on surface, substitutional atom on surface and bulk materials, and vacancy on surface and bulk materials have been studied extensively.
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MOSHER, D., B. V. WEBER, B. MOOSMAN, R. J. COMMISSO, P. COLEMAN, E. WAISMAN, H. SZE, et al. "Measurement and analysis of gas-puff density distributions for plasma radiation source z pinches." Laser and Particle Beams 19, no. 4 (October 2001): 579–95. http://dx.doi.org/10.1017/s026303460119405x.
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High-sensitivity interferometry measurements of initial density distributions are reviewed for a wide range of gas-puff nozzles used in plasma radiation source (PRS) z-pinch experiments. Accurate gas distributions are required for determining experimental load parameters, modeling implosion dynamics, understanding the radiation properties of the stagnated pinch, and for predicting PRS performance in future experiments. For a number of these nozzles, a simple ballistic-gas-flow model (BFM) has been used to provide good physics-based analytic fits to the measured r, z density distributions. These BFM fits provide a convenient means to smoothly interpolate radial density distributions between discrete axial measurement locations for finer-zoned two-dimensional MHD calculations, and can be used to determine how changes in nozzle parameters and load geometry might alter implosion dynamics and radiation performance. These measurement and analysis techniques are demonstrated for a nested-shell nozzle used in Double Eagle and Saturn experiments. For this nozzle, the analysis suggests load modifications that may increase the K-shell yield.
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Jiang, Yingyan, Hua Su, Wei Wei, Yongjie Wang, Hong-Yuan Chen, and Wei Wang. "Tracking the rotation of single CdS nanorods during photocatalysis with surface plasmon resonance microscopy." Proceedings of the National Academy of Sciences 116, no. 14 (March 14, 2019): 6630–34. http://dx.doi.org/10.1073/pnas.1820114116.
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While rotational dynamics of anisotropic nanoobjects has often been limited in plasmonic and fluorescent nanomaterials, here we demonstrate the capability of a surface plasmon resonance microscopy (SPRM) to determine the orientation of all kinds of anisotropic nanomaterials. By taking CdS nanorods as an example, it was found that two-dimensional Fourier transform of the asymmetrical wave-like SPRM image resulted in a peak in its angular spectrum inkspace. Consistency between the peak angle and the geometrical orientation of the nanorod was validated by both in situ scanning electron microscope characterizations and theoretical calculations. Real-time monitoring of the rotational dynamics of single CdS nanorods further revealed the accelerated rotation under appropriate reaction conditions for photocatalyzed hydrogen generation. The driving force was attributed to the asymmetric production of hydrogen molecules as a result of inhomogeneous distribution of reactive sites within the nanorod. The present work not only builds the experimental and theoretical connections between the orientation of anisotropic nanomaterials and its SPRM images; the general suitability of SPRM also sheds light on broad types of nonfluorescent and nonplasmonic anisotropic nanoobjects from semiconductors to bacteria and viruses.
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Li, Jun, Yuhong Huang, Hongkuan Yuan, and Hong Chen. "Predicted hexagonal titanium nitride monolayer as an intrinsic ferromagnetic semiconductor." European Physical Journal Applied Physics 95, no. 1 (July 2021): 10601. http://dx.doi.org/10.1051/epjap/2021210025.
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Two-dimensional (2D) magnetic semiconductors have great promising for energy-efficient ultracompact spintronics due to the low-dimensional ferromagnetic and semiconducting behavior. Here, we predict hexagonal titanium nitride monolayer (h-TiN) to be a ferromagnetic semiconductor by investigating stability, magnetism, and carrier transport of h-TiN using the first-principles calculations. The thermodynamical stability of h-TiN is revealed by phonon dispersion, molecular dynamics simulation and formation energy. The energy band structure shows that h-TiN is a ferromagnetic semiconductor with medium magnetic anisotropy, the magnetic moment of 1μB and the band gaps of 1.33 and 4.42 eV for spin-up and -down channels, respectively. The Curie temperature of h-TiN is estimated to be about 205 K by mean-field theory and not enhanced by the compressive and tensile strains. Higher carrier mobility, in-plane stiffness and conductivity indicate that h-TiN has favorable transport performance. The ferromagnetic semiconducting behavior is robust against the external strains, indicating that h-TiN could be a rare candidate for nanoscale spintronic devices.
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Patrizi, Barbara, Concetta Cozza, Adriana Pietropaolo, Paolo Foggi, and Mario Siciliani de Cumis. "Synergistic Approach of Ultrafast Spectroscopy and Molecular Simulations in the Characterization of Intramolecular Charge Transfer in Push-Pull Molecules." Molecules 25, no. 2 (January 20, 2020): 430. http://dx.doi.org/10.3390/molecules25020430.
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The comprehensive characterization of Intramolecular Charge Transfer (ICT) stemming in push-pull molecules with a delocalized π-system of electrons is noteworthy for a bespoke design of organic materials, spanning widespread applications from photovoltaics to nanomedicine imaging devices. Photo-induced ICT is characterized by structural reorganizations, which allows the molecule to adapt to the new electronic density distribution. Herein, we discuss recent photophysical advances combined with recent progresses in the computational chemistry of photoactive molecular ensembles. We focus the discussion on femtosecond Transient Absorption Spectroscopy (TAS) enabling us to follow the transition from a Locally Excited (LE) state to the ICT and to understand how the environment polarity influences radiative and non-radiative decay mechanisms. In many cases, the charge transfer transition is accompanied by structural rearrangements, such as the twisting or molecule planarization. The possibility of an accurate prediction of the charge-transfer occurring in complex molecules and molecular materials represents an enormous advantage in guiding new molecular and materials design. We briefly report on recent advances in ultrafast multidimensional spectroscopy, in particular, Two-Dimensional Electronic Spectroscopy (2DES), in unraveling the ICT nature of push-pull molecular systems. A theoretical description at the atomistic level of photo-induced molecular transitions can predict with reasonable accuracy the properties of photoactive molecules. In this framework, the review includes a discussion on the advances from simulation and modeling, which have provided, over the years, significant information on photoexcitation, emission, charge-transport, and decay pathways. Density Functional Theory (DFT) coupled with the Time-Dependent (TD) framework can describe electronic properties and dynamics for a limited system size. More recently, Machine Learning (ML) or deep learning approaches, as well as free-energy simulations containing excited state potentials, can speed up the calculations with transferable accuracy to more complex molecules with extended system size. A perspective on combining ultrafast spectroscopy with molecular simulations is foreseen for optimizing the design of photoactive compounds with tunable properties.
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Belchior, J. C., J. P. Braga, and N. HT Lemes. "Classical analysis of intermolecular potentials for ArCO2 rotational collisions." Canadian Journal of Chemistry 79, no. 2 (February 1, 2001): 211–20. http://dx.doi.org/10.1139/v00-165.
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Classical trajectory calculations have been performed for four potential energy functions to describe ArCO2 collisions. A comparison is given between classical cross sections calculated using the two most recent potential surfaces and two older intermolecular potential surfaces based on the electron gas model. The two-dimensional atom ellipsoid model has also been applied for the study of multiple collisions. The model was able to predict such a phenomenon in agreement with quantum scattering results previously published for an ab initio potential surface in the region of very low collision energy. On the other hand, the two older potentials showed multiple collision effects at very high energies. The comparison of the cross sections showed some deviations from the experimental data. By introducing two parameters, a modified surface is proposed by changing the most recent intermolecular potential. In this case the agreement with experimental measurements and theoretical scattering cross sections was considerably improved. It is concluded that global potential surfaces for describing ArCO2 interaction are not well established. To achieve the requirement of reproducing all properties of this system, the present work suggests that one needs further experimental and theoretical investigations. Key words: classical trajectories, dynamics, cross sections, ArCO2 collisions, potentials.
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NANBU, SHINKOH, MUTSUMI AOYAGI, HIDEYUKI KAMISAKA, HIROKI NAKAMURA, WENSHENG BIAN, and KYOSHI TANAKA. "CHEMICAL REACTIONS IN THE O(1D) + HCl SYSTEM I." Journal of Theoretical and Computational Chemistry 01, no. 02 (October 2002): 263–73. http://dx.doi.org/10.1142/s0219633602000191.
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New global ab initio potential energy surfaces (PES) are presented for the low-lying 11A′, 11A′′ and 21A′ electronic states which are correlated to O (1D) + HCl . These potential energy surfaces are computed by using the multi-reference configuration interaction method with the Davidson correction (MRCI+Q). The reference functions are constructed by the complete active space self-consistent field (CASSCF) calculations using the quadruple zeta + polarization basis set augmented with diffuse functions. The computations are carried out at about 5000 molecular conformations on each three-dimensional potential energy surface. The high accuracy of the computations is confirmed by a comparison with the available most accurate data for the ground state 11A′; thus the present work is the first report of the accurate potential energy surfaces for the two excited states. Three low-lying transition states on the excited surfaces, two (TS2 and TS4) on 11A′′ and one (TS3) on 21A′, are found. Since TS2 and TS3 are as low as 0.07 eV and 0.28 eV, respectively, and correlate to the OH (2Π) + Cl (2P) product, these excited surfaces are expected to play quite important roles in the reaction dynamics. Possible effects of nonadiabatic couplings among the three PESs are also briefy discussed, although the nonadiabatic couplings have not yet been estimated. The quantum reaction dynamics on these three PESs are discussed in the second accompanying paper, Paper II.
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Hoch, Laura B., Paul Szymanski, Kulbir Kaur Ghuman, Le He, Kristine Liao, Qiao Qiao, Laura M. Reyes, et al. "Carrier dynamics and the role of surface defects: Designing a photocatalyst for gas-phase CO2 reduction." Proceedings of the National Academy of Sciences 113, no. 50 (November 28, 2016): E8011—E8020. http://dx.doi.org/10.1073/pnas.1609374113.
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In2O3-x(OH)y nanoparticles have been shown to function as an effective gas-phase photocatalyst for the reduction of CO2 to CO via the reverse water–gas shift reaction. Their photocatalytic activity is strongly correlated to the number of oxygen vacancy and hydroxide defects present in the system. To better understand how such defects interact with photogenerated electrons and holes in these materials, we have studied the relaxation dynamics of In2O3-x(OH)y nanoparticles with varying concentration of defects using two different excitation energies corresponding to above-band-gap (318-nm) and near-band-gap (405-nm) excitations. Our results demonstrate that defects play a significant role in the excited-state, charge relaxation pathways. Higher defect concentrations result in longer excited-state lifetimes, which are attributed to improved charge separation. This correlates well with the observed trends in the photocatalytic activity. These results are further supported by density-functional theory calculations, which confirm the positions of oxygen vacancy and hydroxide defect states within the optical band gap of indium oxide. This enhanced understanding of the role these defects play in determining the optoelectronic properties and charge carrier dynamics can provide valuable insight toward the rational development of more efficient photocatalytic materials for CO2 reduction.
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Pileni, M. P. "Fabrication and physical properties of self-organized silver nanocrystals." Pure and Applied Chemistry 72, no. 1-2 (January 1, 2000): 53–65. http://dx.doi.org/10.1351/pac200072010053.
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A simple method is used to prepare highly monodispersed silver nanoparticles in the liquid phase, which starts from an initial synthesis in functionalized AOT reverse micelles. To narrow the particle size distribution from 43 to 12.5% in dispersion, the particles are extracted from the micellar solution. The size-selected precipitation method is used. The nanocrystallites dispersed in hexane are deposited on a support. A monolayer made of nanoparticles with spontaneous compact hexagonal organization is observed. The immersion of the support on the solution yields to the formation of organized multilayers arranged as microcrystal in a face-centered-cubic structure. We compare the optical properties of spherical particles organized in a two- and three-dimensional structure with isolated and disordered particles. When particles, deposited on cleaved graphite, are arranged in a hexagonal array, the optical measurements under p-polarization show a new high-energy resonance, which is interpreted as a collective effect, resulting from optical anisotropy due to the mutual interactions between particles. We support this interpretation by numerical calculations performed for finite-size clusters of silver spheres. For disordered particles, a low-energy resonance appears instead of the high-energy resonance observed for spherical and organized particles. This is interpreted as optical shape anisotropy due to the asymmetrical arrangement of particles. The tip of a scanning tunneling microscope (STM) may be used as an extremely localized source of low-energy electrons to locally excite photon emission from a variety of metal films. The detection of locally excited luminescence at the junction of an STM tip provides access to electron dynamic properties at the surface, which makes it possible to study luminescence phenomena of nanometer-sized structures. The photon intensity emitted from electrically isolated silver nanoparticles self-organized as a 2D network on a gold (111) substrate is analyzed. We observed unexpectedly strong variations of photon-emission efficiency from isolated nanoparticles, depending on how tightly they are embedded within the network site. The quenching site observed in the STM photon emission map is interpreted as an enhanced interaction of electrons with surface photon modes.
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Wang, Ai, Jamshid Ashurov, Aziz Ibragimov, Ruimin Wang, Halima Mouhib, Nasir Mukhamedov, and Ulli Englert. "Charge density of the biologically active molecule (2-oxo-1,3-benzoxazol-3(2H)-yl)acetic acid." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 72, no. 1 (January 29, 2016): 142–50. http://dx.doi.org/10.1107/s2052520615023690.
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(2-Oxo-1,3-benzoxazol-3(2H)-yl)acetic acid is a member of a biologically active class of compounds. Its molecular structure in the crystal has been determined by X-ray diffraction, and its gas phase structure was obtained by quantum chemical calculations at the B3LYP/6-311++G(d,p) level of theory. In order to understand the dynamics of the molecule, two presumably soft degrees of freedom associated with the relative orientation of the planar benzoxazolone system and its substituent at the N atom were varied systematically. Five conformers have been identified as local minima on the resulting two-dimensional potential energy surface within an energy window of 27 kJ mol−1. The energetically most favourable minimum closely matches the conformation observed in the crystal. Based on high-resolution diffraction data collected at low temperature, the experimental electron density of the compound was determined. Comparison with the electron density established by theory for the isolated molecule allowed the effect of intermolecular interactions to be addressed, in particular a moderately strong O—H...O hydrogen bond with a donor...acceptor distance of 2.6177 (9) Å: the oxygen acceptor is clearly polarized in the extended solid. The hydrogen bond connects consecutive molecules to chains, and the pronounced charge separation leads to stacking between neighburs with antiparallel dipole moments perpendicular to the chain direction.
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Klein, Richard I., and Jonathan Arons. "Radiation Gas Dynamics of Polar Cap Accretion onto Magnetized Neutron Stars." Symposium - International Astronomical Union 125 (1987): 246. http://dx.doi.org/10.1017/s0074180900160826.
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We present results of the first self-consistent, time-dependent, 2-D calculations of the accretion of plasma onto polar caps of high luminosity (L*>1036erg-s−1) magnetized neutron stars. We follow the temporal and spatial evolution of three fluids, electrons, ions and photons in a superstrong (B=3×1012 Gauss) dipole magnetic field where radiation pressure dominates plasma pressure by solving coupled 2-D equations of radiation hydrodynamics. We have included several physical processes in the radiation-plasma coupling in superstrong magnetic fields (Klein, et al., 1984, Santa Cruz Workshop on High Energy Transients, and Arons, this conference). We solve the resulting system of coupled 2-D PDEs on a Cray XMP-48 by applying implicit finite-difference techniques with iterative operator splitting methods. We present results for two models of 5×1037 erg-s and 1.5×1038 erg-s−1 super-Eddington luminosity on one polar cap, each having initial mass flux independent of co-latitude of a field lines footprint. We find (a) Radiation develops a broad transverse fan beam that emerges from an annulus 0.2–0.5km above the polar cap. (b) The beam profile is determined by advective trapping of radiation in optically thick (τ11,τ⊥ ≈103) flow. Here the time for diffusion of radiation up through the accretion column is ≫ the time for downward advection. (c) There is a three fluid nonequilibrium with Ti≫Tγ≥Te. (d) Maximum photon temperature of ≈ 10–20 keV in the fan beam is in the observed range. (e) Cyclotron emission ≫ bremsstrahlung as a source of photons. (f) At early times (≪lms) radiation pressure strongly decelerates flow to 10−3 of freefall in central regions of accretion column resulting in a density mound, but plasma freefalls down the sides of the column. (g) Analytical models have reasonable agreement with numerical calculations; velocity and energy density roughly Gaussian transversally and exponential vertically, until the onset of “photon bubbles” after several dynamical times (∼lms). (h) Multiple “photon bubbles” rising subsonically in the accretion column form in the high luminosity model. We believe the photon bubbles to be a possible consequence of overstable convection in super-Eddington flows. These photon bubbles could be observable as 10–100μs fluctuations in the emergent flux and, thus, be an important diagnostic for inhomogeneous structure of the column.
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Borchardt, Norman, and Roland Kasper. "Parametric model of electric machines based on exponential Fourier approximations of magnetic air gap flux density and inductance." COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 37, no. 1 (January 2, 2018): 520–35. http://dx.doi.org/10.1108/compel-06-2017-0251.
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Purpose This study aims to present a parametric model of a novel electrical machine, based on a slotless air gap winding, allowing for fast and precise magnetic circuit calculations. Design/methodology/approach Approximations of Fourier coefficients through an exponential function deliver the required nonlinear air gap flux density and inductance. Accordingly, major machine characteristics, such as back-EMF and torque, can be calculated analytically with high speed and precision. A physical model of the electrical machine with air gap windings is given. It is based on a finite element analysis of the air gap magnetic flux density and inductance. The air gap height and the permanent magnetic height are considered as magnetic circuit parameters. Findings In total, 11 Fourier coefficient matrixes with 65 sampling points each were generated. From each, matrix a two-dimensional surface function was approximated by using exponentials. Optimal parameters were calculated by the least-squares method. Comparison with the finite element model demonstrates a very low error of the analytical approximation for all Fourier coefficients considered. Finally, the dynamics of an electrical machine, modeled using the preceding magnetic flux density approximation, are analyzed in MATLAB Simulink. Required approximations of the phase self-inductance and mutual inductance were given. Accordingly, the effects of the two magnetic circuit parameters on the dynamics of electrical machine current as well as the electrical machine torque are explained. Originality/value The presented model offers high accuracy comparable to FE-models, needing only very limited computational complexity.
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Breuillard, H., Y. Zaliznyak, V. Krasnoselskikh, O. Agapitov, A. Artemyev, and G. Rolland. "Chorus wave-normal statistics in the Earth's radiation belts from ray tracing technique." Annales Geophysicae 30, no. 8 (August 21, 2012): 1223–33. http://dx.doi.org/10.5194/angeo-30-1223-2012.
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Abstract. Discrete ELF/VLF (Extremely Low Frequency/Very Low Frequency) chorus emissions are one of the most intense electromagnetic plasma waves observed in radiation belts and in the outer terrestrial magnetosphere. These waves play a crucial role in the dynamics of radiation belts, and are responsible for the loss and the acceleration of energetic electrons. The objective of our study is to reconstruct the realistic distribution of chorus wave-normals in radiation belts for all magnetic latitudes. To achieve this aim, the data from the electric and magnetic field measurements onboard Cluster satellite are used to determine the wave-vector distribution of the chorus signal around the equator region. Then the propagation of such a wave packet is modeled using three-dimensional ray tracing technique, which employs K. Rönnmark's WHAMP to solve hot plasma dispersion relation along the wave packet trajectory. The observed chorus wave distributions close to waves source are first fitted to form the initial conditions which then propagate numerically through the inner magnetosphere in the frame of the WKB approximation. Ray tracing technique allows one to reconstruct wave packet properties (electric and magnetic fields, width of the wave packet in k-space, etc.) along the propagation path. The calculations show the spatial spreading of the signal energy due to propagation in the inhomogeneous and anisotropic magnetized plasma. Comparison of wave-normal distribution obtained from ray tracing technique with Cluster observations up to 40° latitude demonstrates the reliability of our approach and applied numerical schemes.
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Sanborn, B. A. "Total Dielectric Function Approach to the Electron Boltzmann Equation for Scattering from a Two-Dimensional Coupled Mode System." VLSI Design 6, no. 1-4 (January 1, 1998): 69–72. http://dx.doi.org/10.1155/1998/70276.
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The nonequilibrium total dielectric function lends itself to a simple and general method for calculating the inelastic collision term in the electron Boltzmann equation for scattering from a coupled mode system. Useful applications include scattering from plasmon-polar phonon hybrid modes in modulation doped semiconductor structures. This paper presents numerical methods for including inelastic scattering at momentum-dependent hybrid phonon frequencies in the low-field Boltzmann equation for two-dimensional electrons coupled to bulk phonons. Results for electron mobility in GaAs show that the influence of mode coupling and dynamical screening on electron scattering from polar optical phonons is stronger for two dimensional electrons than was previously found for the three dimensional case.
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Karkina, Lidia, Iliya Karkin, Andrey Kuznetsov, and Yuri Gornostyrev. "Alloying Element Segregation and Grain Boundary Reconstruction, Atomistic Modeling." Metals 9, no. 12 (December 6, 2019): 1319. http://dx.doi.org/10.3390/met9121319.
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Grain boundary (GB) segregation is an important phenomenon that affects many physical properties, as well as microstructure of polycrystals. The segregation of solute atoms on GBs and its effect on GB structure in Al were investigated using two approaches: First principles total energy calculations and the finite temperature large-scale atomistic modeling within hybrid MD/MC approach comprising molecular dynamics and Monte Carlo simulations. We show that the character of chemical bonding is essential in the solute–GB interaction, and that formation of directed quasi-covalent bonds between Si and Zn solutes and neighboring Al atoms causes a significant reconstruction of the GB structure involving a GB shear-migration coupling. For the solutes that are acceptors of electrons in the Al matrix and have a bigger atomic size (such as Mg), the preferred position is determined by the presence of extra volume at the GB and/or reduced number of the nearest neighbors; in this case, the symmetric GB keeps its structure. By using MD/MC approach, we found that GBs undergo significant structural reconstruction during segregation, which can involve the formation of single- or double-layer segregations, GB splitting, and coupled shear-migration, depending on the details of interatomic interactions.
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Borzehandani, Mostafa Yousefzadeh, Emilia Abdulmalek, Mohd Basyaruddin Abdul Rahman, and Muhammad Alif Mohammad Latif. "Elucidating the Aromatic Properties of Covalent Organic Frameworks Surface for Enhanced Polar Solvent Adsorption." Polymers 13, no. 11 (June 3, 2021): 1861. http://dx.doi.org/10.3390/polym13111861.
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Covalent organic frameworks (COFs) have a distinguished surface as they are mostly made by boron, carbon, nitrogen and oxygen. Many applications of COFs rely on polarity, size, charge, stability and hydrophobicity/hydrophilicity of their surface. In this study, two frequently used COFs sheets, COF-1 and covalent triazine-based frameworks (CTF-1), are studied. In addition, a theoretical porous graphene (TPG) was included for comparison purposes. The three solid sheets were investigated for aromaticity and stability using quantum mechanics calculations and their ability for water and ethanol adsorption using molecular dynamics simulations. COF-1 demonstrated the poorest aromatic character due to the highest energy delocalization interaction between B–O bonding orbital of sigma type and unfilled valence-shell nonbonding of boron. CTF-1 was identified as the least kinetically stable and the most chemically reactive. Both COF-1 and CTF-1 showed good surface properties for selective adsorption of water via hydrogen bonding and electrostatic interactions. Among the three sheets, TPG’s surface was mostly affected by aromatic currents and localized π electrons on the phenyl rings which in turn made it the best platform for selective adsorption of ethanol via van der Waals interactions. These results can serve as guidelines for future studies on solvent adsorption for COFs materials.
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Yu, Tsung-Hsing, and Kevin F. Brennan. "Monte Carlo calculation of two-dimensional electron dynamics in GaN–AlGaN heterostructures." Journal of Applied Physics 91, no. 6 (March 15, 2002): 3730–36. http://dx.doi.org/10.1063/1.1448889.
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ZASPEL, C. E., and JOHN E. DRUMHELLER. "ELECTRON PARAMAGNETIC RESONANCE DETECTION OF SOLITONS IN TWO-DIMENSIONAL MAGNETS." International Journal of Modern Physics B 10, no. 27 (December 15, 1996): 3649–71. http://dx.doi.org/10.1142/s0217979296001987.
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It has previously been assumed that spin waves were the dominant excitations in lower-dimensional magnets. Recently, however, it has been shown that nonlinear excitations or solitons rather than spin waves influence the dynamic thermal quantities such as the spin correlation function which can be investigated experimentally through the electron paramagnetic resonance linewidth. In this review the influence of both spin waves and solitons on the temperature-dependent linewidth in the fluctuation region immediately above the ordering temperature is discussed. It is seen that both excitations result in a theoretical Arrhenius temperature-dependence, (∆H~ exp (E/T) where E=6πJs2 for spin waves and E=4πJs2 for solitons, J is the nearest neighbor exchange constant, and s is the value of the spin. In experiments, quantum (s=1/2) layered copper compounds exhibit the temperature dependence expected from spin waves even though nonlinear excitations have been shown to exist in these systems. On the other hand nearly classical (s=5/2) manganese compounds have the temperature dependence expected from solitons. The calculation of the linewidth from both spin waves and solitons is reviewed and compared with experimental data to show that solitons dominate the dynamics of the layered, nearly classical magnet.
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SHARMA, A. C., and A. BAJPAI. "DYNAMICAL CONDUCTIVITY OF LOW-DIMENSIONAL SYSTEMS." International Journal of Modern Physics B 16, no. 10 (April 20, 2002): 1511–31. http://dx.doi.org/10.1142/s0217979202010294.
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A calculation of dynamical conductivity is performed for low-dimensional systems, by taking into account the screening of field. Our calculation is valid for all value of wave vector and frequency. The Drude conductivity of three, two and one-dimensional free electron gas, layered electron gas and quantum wire system can be deduced from our calculation. However, our calculation suggests that the use of Drude formulae of conductivity to explain experimental result on microwave and infra-red conductivity, in long wave length limit, can be highly erroneous in case of low-dimensional system that offer larger value of relaxation time. It is found that; (i) screening of a dynamical field becomes less significant on reduction in dimensionality and (ii) unlike the case of three dimensional electron gas, transverse electric field cannot excite collective excitation modes (penetration depth cannot be defined) in a two-dimensional electron gas and quantum wire system. In comparison with prior reported calculation ours is more rigorous calculation as it includes the possibility of propagation of collective excitation modes in all direction. The plasmons in a low-dimensional system cannot be excited for negligibly small value of momentum transfer.
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Bilgeç Akyüz, G., A. Siddiki, and İ. Sökmen. "Magnetotransport calculations for two-dimensional electrons with exchange and correlation interactions." Physica E: Low-dimensional Systems and Nanostructures 69 (May 2015): 364–70. http://dx.doi.org/10.1016/j.physe.2015.02.009.
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BANG, Junhyeok. "Excited Carrier Dynamics in Two-dimensional Materials." Physics and High Technology 29, no. 9 (September 30, 2020): 15–21. http://dx.doi.org/10.3938/phit.29.032.
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When electrons in materials are excited, they undergo several dynamic processes such as carrier thermalization, transfer, and recombination. These fundamental excited state processes are crucial to understanding the microscopic principles at work in electronic and optoelectronic devices. This article introduces the excited carrier dynamics in a two-dimensional van der Waals material and reveals several interesting phenomena that do not occur in bulk materials. Particularly, the focus will be two dynamic processes: carrier multiplication and ultrafast charge transfer.
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Eaglesham, D. J. "Perturbation theory for dynamical diffraction calculations." Proceedings, annual meeting, Electron Microscopy Society of America 47 (August 6, 1989): 482–83. http://dx.doi.org/10.1017/s042482010015438x.
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The dynamical diffraction of high-energy electrons may be calculated to a fair degree of accuracy by several methods. The most widespread techniques involve either multislice calculations or Bloch wave diagonalisation, the two giving equivalent results for diffracted beam intensities for a given set of conditions. However, both types of calculation are approximate, in that they involve a truncated expansion (of not only the electron wavefunction but also the crystal potential) in the number of diffracting beams. Bloch wave diagonalisations, for example, involve computation times which increase as the cube of the number of beams included in the calculation, so that truncation of the calculation with the smallest possible number of beams is essential. Unfortunately, dynamical diffraction calculations (using either multislice or diagonalisation) tend to converge extremely slowly with increasing number of beams, so that Bloch wave calculations in particular can be highly time-consuming. In addition, it is generally difficult to estimate the magnitude of the systematic errors that truncation has produced. However, the scattering to the outermost beams is generally weak, suggesting that these higher coefficients of the potential may be treated within perturbation theory. The pupose of this paper is to present the equations for a perturbation treatment of truncation.
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Towler, M. D., N. J. Russell, and Antony Valentini. "Time scales for dynamical relaxation to the Born rule." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 468, no. 2140 (November 30, 2011): 990–1013. http://dx.doi.org/10.1098/rspa.2011.0598.
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We illustrate through explicit numerical calculations how the Born rule probability densities of non-relativistic quantum mechanics emerge naturally from the particle dynamics of de Broglie–Bohm pilot-wave theory. The time evolution of a particle distribution initially not equal to the absolute square of the wave function is calculated for a particle in a two-dimensional infinite potential square well. Under the de Broglie–Bohm ontology, the box contains an objectively existing ‘pilot wave’ which guides the electron trajectory, and this is represented mathematically by a Schrödinger wave function composed of a finite out-of-phase superposition of M energy eigenstates (with M ranging from 4 to 64). The electron density distributions are found to evolve naturally into the Born rule ones and stay there; in analogy with the classical case this represents a decay to ‘quantum equilibrium’. The proximity to equilibrium is characterized by the coarse-grained subquantum H -function which is found to decrease roughly exponentially towards zero over the course of time. The time scale τ for this relaxation is calculated for various values of M and the coarse-graining length ε . Its dependence on M is found to disagree with an earlier theoretical prediction. A power law, τ ∝ M −1 , is found to be fairly robust for all coarse-graining lengths and, although a weak dependence of τ on ε is observed, it does not appear to follow any straightforward scaling. A theoretical analysis is presented to explain these results. This improvement in our understanding of time scales for relaxation to quantum equilibrium is likely to be of use in the development of models of relaxation in the early Universe, with a view to constraining possible violations of the Born rule in inflationary cosmology.
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Duke, Jessica Ryan, and Nandini Ananth. "Mean field ring polymer molecular dynamics for electronically nonadiabatic reaction rates." Faraday Discussions 195 (2016): 253–68. http://dx.doi.org/10.1039/c6fd00123h.
Full textAbstract:
We present a mean field ring polymer molecular dynamics method to calculate the rate of electron transfer (ET) in multi-state, multi-electron condensed-phase processes. Our approach involves calculating a transition state theory (TST) estimate to the rate using an exact path integral in discrete electronic states and continuous Cartesian nuclear coordinates. A dynamic recrossing correction to the TST rate is then obtained from real-time dynamics simulations using mean field ring polymer molecular dynamics. We employ two different reaction coordinates in our simulations and show that, despite the use of mean field dynamics, the use of an accurate dividing surface to compute TST rates allows us to achieve remarkable agreement with Fermi's golden rule rates for nonadiabatic ET in the normal regime of Marcus theory. Further, we show that using a reaction coordinate based on electronic state populations allows us to capture the turnover in rates for ET in the Marcus inverted regime.
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Błasiak, Przemysław, Marcin Opalski, Parthkumar Parmar, Cezary Czajkowski, and Sławomir Pietrowicz. "The Thermal—Flow Processes and Flow Pattern in a Pulsating Heat Pipe—Numerical Modelling and Experimental Validation." Energies 14, no. 18 (September 19, 2021): 5952. http://dx.doi.org/10.3390/en14185952.
Full textAbstract:
The aim of the article is to numerically model a two-dimensional multiphase flow based on the volume of fluid method (VOF) in a pulsating heat pipe (PHP). The current state of knowledge regarding the modeling of these devices was studied and summarised. The proposed model is developed within open source software, OpenFOAM, based on the predefined solver called interPhaseChangeFoam. The analyses were carried out in terms of the influence of four different mass transfer models between the phases, proposed by Tanasawa, Lee, Kafeel and Turan, and Xu et al. on the shape and dynamics of the internal flow structures. The numerical models were validated against data obtained from a specially designed experimental setup, consisting of three bends of pulsating heat pipes. The numerical calculations were carried out with ethanol being treated as a working medium and the initial and boundary conditions taken directly from the measurement procedures. The variable input parameter for the model was the heat flux implemented in the evaporation section and a fixed temperature applied to the condensation section. The flow structures obtained from the numerical analyses were compared and discussed with the flow structures gained from experimental studies by employing a high speed camera. In addition, to verify the quantitative results obtained from the numerical analyses with the experimental data, a technique called particle image velocimetry (PIV) was used for the velocity vector field. For the analysed velocity ranges, the relative error obtained was reached at the level of 10%.
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Yu, Renwen, and F. Javier García de Abajo. "Chemical identification through two-dimensional electron energy-loss spectroscopy." Science Advances 6, no. 28 (July 2020): eabb4713. http://dx.doi.org/10.1126/sciadv.abb4713.
Full textAbstract:
We explore a disruptive approach to nanoscale sensing by performing electron energy loss spectroscopy through the use of low-energy ballistic electrons that propagate on a two-dimensional semiconductor. In analogy to free-space electron microscopy, we show that the presence of analyte molecules in the vicinity of the semiconductor produces substantial energy losses in the electrons, which can be resolved by energy-selective electron injection and detection through actively controlled potential gates. The infrared excitation spectra of the molecules are thereby gathered in this electronic device, enabling the identification of chemical species with high sensitivity. Our realistic theoretical calculations demonstrate the superiority of this technique for molecular sensing, capable of performing spectral identification at the zeptomol level within a microscopic all-electrical device.