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1.
In this paper, we report on a series of computational simulations on hydrogen bonding in two ice phases (Ih and Ic) using CASTEP with PW91 and RPBE exchange-correlation based on ab initio density functional theory. The strength of the H-bond is correlated with intramolecular O-H stretching, and the energy splitting exists for both the H-bond and covalent O-H stretching. By analyzing the dispersion relationship of to(q), we observe the separation of the longitudinal optic (LO) mode from transverse optic (TO) mode at the gamma point, seemingly interpreting the controversial two H-bond peaks in the vibrational spectrum of ice recorded by inelastic incoherent neutron scattering experiments. The test of ambient environment on phonon density of sates (PDOS) shows that the relaxed tetrahedral structure is the most stable structural configuration for water clusters. 相似文献
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We report high-temperature thermodynamics for fcc silver by combining ab initio phonon dynamics to empirical quadratic temperature-dependent term for anharmonic part of Helmholtz free energy. The electronic free energy is added through an interpolation scheme, which connects ambient condition free electron gas model to Thomas-Fermi results.The present study shows good agreement with experimental and reported findings for several thermal properties, and the discrepancy observed in some caloric properties is addressed. The decreases in the product of volume thermal expansion coefficient and isothermal bulk modulus and in the constant volume anharmonic lattice specific heat at high temperature are the clear evidences of proper account of anharmonicity. The present study also reveals that T~2-dependent anharmonic free energy is sufficient for correct evaluation of thermal pressure and conventional Grüneisen parameter. We observe that the intrinsic phonon anharmonicity starts dominating above characteristic temperature, which is attributed to higher order anharmonicity and can be related to higher order potential derivatives. We conclude that the uncorrelated and largeamplitude lattice vibrations at high temperature raise dominating intrinsic thermal stress mechanism, which surpasses the phonon-anharmonism and requires future consideration. 相似文献
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Frontiers of Physics - Results of inelastic neutron scattering experiments and ab initio molecular dynamics simulations for GeTe–the parent compound of phase-change materials are reported.... 相似文献
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In this paper Monte Carlo simulations of a dissociative electron transfer reaction in solution have been performed in order to test to what extent the deviation of Marcus' relationship for this kind of reactions can be attributed to the features of the solute internal potential energy. It is shown that Marcus' equation does not apply to this kind of dissociative electron transfer processes if the ab initio solute internal potential energies are used. Conversely, if a Morse curve and its repulsive part are employed to describe the solute internal potential energies, Marcus' relationship is recovered. Then, the problem is reduced to what extent the ab initio solute internal potential energies can be represented by Morse curves. 相似文献
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Ab initio approaches are among the most advanced models to solve the nuclear many-body problem. In particular, the no-core–shell model and many-body perturbation theory have been recently extended to the Gamow shell model framework, where the harmonic oscillator basis is replaced by a basis bearing bound, resonance and scattering states, i.e. the Berggren basis. As continuum coupling is included at basis level and as configuration mixing takes care of inter-nucleon correlations, halo and resonance nuclei can be properly described with the Gamow shell model. The development of the no-core Gamow shell model and the introduction of the $\hat{\bar{Q}}$ -box method in the Gamow shell model, as well as their first ab initio applications, will be reviewed in this paper. Peculiarities compared to models using harmonic oscillator bases will be shortly described. The current power and limitations of ab initio Gamow shell model will also be discussed, as well as its potential for future applications. 相似文献
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We present an introduction to the application of ab initio methods of Quantum Chemistry to the molecular model of atomic collisions. This includes the choice and calculation of molecular wavefunctions using the well known Self Consistent Field and Configuration Interaction methods; the calculation of dynamical couplings and a detailed study of diabatic states. To make the article self contained, we also consider the momentum transfer problem. Papers which we find useful to introduce the different subjects or for further reading are also reviewed. 相似文献
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Chiral symmetry in nuclei 总被引:1,自引:0,他引:1
Effective field theory is considered to provide a highly useful framework for connecting nuclear physics with the symmetries and dynamics of the underlying theory of strong interactions, QCD. Of many issues that are of great current interest in this domain, I concentrate here on two: (1) A new class of ab initio calculations of observables in two-nucleon systems; (2) Attempts to extend chiral perturbation calculations to higher-order terms. 相似文献
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The equations of state (EOS) and other thermodynamic properties of TiB2 are investigated using ab initio plane-wave pseudopotential density functional theory method. The obtained results are in good agreement with the experimental measured data and other theoretical calculated ones. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V/V0 on pressure P, cell volume V on temperature T, and Debye temperature Θ and specific heat CV on pressure P are successfully obtained. 相似文献
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The equations of state (EOS) and other thermodynamic properties of the rocksalt (RS) structure MgO are investigated by ab initio plane-wave pseudopotential density functional theory method. The obtained results are consistent with the experimental data and those calculated by others. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V/V0 on pressure P, cell volume V on temperature T, and Debye temperature Θ and specific heat CV on pressure P are successfully obtained. The variation of the thermal expansion with temperature and pressure is investigated, which shows the temperature has hardly any effect on the thermal expansion at higher pressure. 相似文献
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Yong-Peng Shi 《中国物理 B》2021,30(12):126105-126105
The U-Nb alloy, as a kind of nuclear material with good corrosion resistance and mechanical properties, plays an important role in the nuclear industry. However, the experimental measurements and theoretical calculations of many parameters which are essential in describing the dynamical properties of this alloy melt, including density, diffusivity, and viscosity, have not been carried out yet. The lack of data on the dynamical properties of nuclear materials seriously hinders the high-performance nuclear materials from being developed and applied. In this work, the dynamical properties of the U-Nb alloy melt are systematically studied by means of ab initio molecular dynamics simulations and their corresponding mathematical models are established, thereby being able to rapidly calculate the densities, diffusion coefficients, viscosities, and their activation energies in the whole U-Nb liquid region. This work provides a new idea for investigating the dynamical properties of binary alloy melts, thereby promoting the development of melt research. 相似文献
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A. V. Rybina V. V. Efimov P. A. Alekseev I. O. Troyanchuk A. S. Ivanov V. V. Sikolenko E. S. Clementyev 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(6):1140-1143
The lattice dynamics of lanthanum cobaltite is investigated using the coherent inelastic neutron scattering technique in a
temperature range from 10 to 536 K, in which two phase transitions are observed: a change in the Co spin state and a metal-insulator
phase transition. The measurements were performed using an IN8 high flux thermal neutron triple-axis spectrometer (ILL, Grenoble).
Temperature changes in the phonon dispersion curves caused by the rearrangement of the electron and spin subsystems are found. 相似文献
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Hui-Li Wang 《Frontiers of Physics》2018,13(3):138107
In order to obtain a comprehensive understanding of both thermodynamics and kinetics of water dissociation on TiO2, the reactions between liquid water and perfect and defective rutile TiO2 (110) surfaces were investigated using ab initio molecular dynamics simulations. The results showed that the free-energy barrier (~4.4 kcal/mol) is too high for a spontaneous dissociation of water on the perfect rutile (110) surface at a low temperature. The most stable oxygen vacancy (Vo1) on the rutile (110) surface cannot promote the dissociation of water, while other unstable oxygen vacancies can significantly enhance the water dissociation rate. This is opposite to the general understanding that Vo1 defects are active sites for water dissociation. Furthermore, we reveal that water dissociation is an exothermic reaction, which demonstrates that the dissociated state of the adsorbed water is thermodynamically favorable for both perfect and defective rutile (110) surfaces. The dissociation adsorption of water can also increase the hydrophilicity of TiO2. 相似文献
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Two-dimensional square-Au_2S monolayer: A promising thermoelectric material with ultralow lattice thermal conductivity and high power factor
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《中国物理 B》2021,30(7):77405-077405
The search for new two-dimensional(2 D) harvesting materials that directly convert(waste) heat into electricity has received increasing attention. In this work, thermoelectric(TE) properties of monolayer square-Au_2S are accurately predicted using a parameter-free ab initio Boltzmann transport formalism with fully considering the spin–orbit coupling(SOC),electron–phonon interactions(EPIs), and phonon–phonon scattering. It is found that the square-Au_2S monolayer is a promising room-temperature TE material with an n-type(p-type) figure of merit ZT = 2.2(1.5) and an unexpected high n-type ZT = 3.8 can be obtained at 600 K. The excellent TE performance of monolayer square-Au_2S can be attributed to the ultralow lattice thermal conductivity originating from the strong anharmonic phonon scattering and high power factor due to the highly dispersive band edges around the Fermi level. Additionally, our analyses demonstrate that the explicit treatments of EPIs and SOC are highly important in predicting the TE properties of monolayer square-Au_2S. The present findings will stimulate further the experimental fabrication of monolayer square-Au_2S-based TE materials and offer an in-depth insight into the effect of SOC and EPIs on TE transport properties. 相似文献
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Douglas L. Dorset 《Micron (Oxford, England : 1993)》1995,26(6):511-520
Applications of the Sayre equation to the electron crystallographic analysis of protein structures are demonstrated. Starting with a lower-resolution basis phase set obtained from the Fourier-transform of an electron micrograph, it is possible, for example, to extend directly to the higher resolution of the electron diffraction pattern. Examples of such analyses include bacteriorhodopsin, halorhodopsin and the Omp F porin from the outer membrane of Eschirichia coli. If a multisolution approach is taken, it may also be possible to carry out ab initio phase determinations, as demonstrated with low-resolution diffraction amplitudes from a negatively-stained membrane protein crystal. 相似文献
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A new global potential energy surface of the ground state of SiH2+ (X2A1) system and dynamics calculations of the Si+ + H2 (v0 = 2, j0 = 0) → SiH+ + H reaction
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Yong Zhang 《中国物理 B》2022,31(11):113101-113101
A global potential energy surface (PES) of the ground state of SiH$_{2}^{+}$ system is built by using neural network method based on 18223 ab initio points. The topographic properties of PES are presented and compared with previous theoretical and experimental studies. The results indicate that the spectroscopic parameters obtained from the new PES are in good agreement with the experimental data. In order to further verify the validity of the new PES, a test dynamics calculation of the Si$^{+} +$ H$_{2}$ ($v_0 = 2, j_{0} = 0$) $\to $ H $+$ SiH$^{+}$ reaction has been carried out by using the time-dependent wave packet method. The integral cross sections and rate constants are computed for the title reaction. The reasonable dynamical behavior indicates that the newly constructed PES is suitable for relevant dynamics investigations. 相似文献
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The elastic properties of zinc-blend (ZB) and rock-salt (RS) MgS are calculated by ab initio method. The calculation shows that the enthalpy for RS structure and for ZB structure essentially is the same at ambient pressure. The ZB structure becomes unstable above 5 GPa. For these two structures, the pressure dependences of typical elastic properties, i.e. the bulk modulus, the shear modulus, the Young's modulus, the Poisson's ratio, and the anisotropy factor, are presented. The Debye temperature and sound velocity under high pressure have also been calculated. Debye approximation is used to estimate the zero-point vibrational energy. 相似文献
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Surface stress relief is often invoked as the driving force for surface reconstruction. The present ab initio total energy calculations show that it is not the case, at least for the missing row reconstruction undergone by the (1 1 0) surface of the face centered cubic transition metals. Instead, they show that the tendency to reconstruct or not is closely related to the sign and magnitude of the strain derivative of surface energy. Finally, they unambiguously confirm that relativistic effects are at the origin of this reconstruction. 相似文献