Dynamics of liquid lithium atoms: Time scales and dynamic correlation functions

© 2020 Polish Academy of Sciences. All rights reserved. Memory functions of the relaxation process of the density fluctuations of the lithium melt near the melting point on the basis of molecular dynamics data are calculated. It is established that the memory functions of the first four orders for the range of wave numbers corresponding to microscopic spatial scales are characterized by oscillating behavior. The frequency characteristics of the dynamic structure factor for a wide range of wave numbers are calculated. The convergence of the relaxation parameters Δ4(k) and Δ5(k) for the range of wave numbers from the hydrodynamic regime (k → 0) to the values of k higher than the boundary of the first pseudo-Brillouin zone (for k ≈ 0:87km) are detected. The characteristic time scales of the process of structural relaxation of the density fluctuations are determined

Dynamics of liquid lithium atoms: Time scales and dynamic correlation functions

© 2020, Education and Upbringing Publishing. All rights reserved. Based on the configuration data on molecular dynamics simulation of the lithium melt near the melting point, the memory functions of the relaxation process of the density fluctuations are calculated. It is established that for the range of wave numbers corresponding to microscopic spatial scales, the memory functions of the first four orders are characterized by oscillating behavior. This feature indicates that the model memory functions in the case of phenomenological description of the dynamics of the density fluctuations can not have the form of monotonically decreasing functions. The frequency characteristics of the dynamic structure factor for a wide range of wave numbers are calculated. The convergence of the relaxation parameters Δ4(k) and Δ5(k) for the range of wave numbers from the hydrodynamic regime (k → 0) to the values of k is higher than the boundary of the first pseudo-Brillouin zone (for k ≈ 0:87km) are detected. The characteristic time scales of the process of structural relaxation of the density fluctuations are determined

Elastic properties and glass forming ability of the zr<inf>50</inf>cu<inf>40</inf>ag<inf>10</inf> metallic alloy

© 2020 Trans Tech Publications Ltd, Switzerland The elastic properties of the Zr50Cu40Ag10 metallic alloy, such as the bulk modulus B, the shear modulus G, the Young’s modulus E and the Poisson’s ratio σ, are investigated by molecular dynamics simulation in the temperature range T=250–2000 K and at an external pressure of p=1.0 bar. It is shown that the liquid–glass transition is accompanied by a considerable increase in the shear modulus G and the Young’s modulus E (by more than 50%). The temperature dependence of the Poisson’s ratio exhibits a sharp fall from typical values for metals of approximately 0.32– 0.33 to low values (close to zero), which are characteristic for brittle bulk metallic glasses. Non-monotonic temperature dependence of the longitudinal and transverse sound velocity near the liquid-glass transition is also observed. The glass forming ability of the alloy is evaluated in terms of the fragility index m. As found, its value is m≈64 for the Zr50Cu40Ag10 metallic glass, that is in a good agreement with the experimental data for the Zr-Cu-based metallic glasses

Electrocrystallization of Supercooled Water in Confinement

© 2020, Pleiades Publishing, Ltd. Abstract: The paper discusses the features of supercooled water thin film of width d = 3.97 nm contained by the perfect graphene layers and crystallizing under external stationary electric field. It was found that the electric field applied perpendicular to graphene layers impedes structural ordering, while the electric field applied in lateral direction contributes to formation of the cubic ice (Ic) phase, which is thermodynamically less stable compared to the hexagonal ice (Ih) phase. It is shown that the growth of the Ic crystalline phase occurs without formation of intermediate crystalline phases. It was found that the crystallization rate depends strongly on the magnitude of the applied electric field. In particular, the processes of full electrocrystallization of the system do not appear over simulation time scale (~40 ns) if the electric field of the magnitude less than 0.07 V/Å is applied

Electronic and Thermophysical Properties of Gas Hydrates: Ab Initio Simulation Results

Abstract: Results of ab initio molecular-dynamic investigation of the electronic and thermophysical properties of methane hydrate with cubic structure sI are represented. The simulation results for specific heat at constant volume and density are in good agreement with experimental data. The temperature dependences of the electronic properties of methane hydrate (including Fermi energy level and width and edges of the band gap) are determined based on analysis of the density of electronic states. For an empty hydrate framework (aqueous clathrate framework), the spectra of electron energy E(k) along the M–X, X–Γ, Γ–M, and Γ–R directions are calculated. It is established that the presence of CH4 molecules in the aqueous clathrate increases the hydrate Fermi energy from 2.4 to 3.0 eV

Quasi-solid state microscopic dynamics in equilibrium classical liquids: Self-consistent relaxation theory

In the framework of the concept of time correlation functions, we develop a self-consistent relaxation theory of the transverse collective particle dynamics in liquids. The theory agrees with well-known results in both the short-wave (free-particle dynamics) and the long-wave (hydrodynamic) limits. We obtain a general expression for the spectral density CT(k, ω) of the transverse particle current realized in a rangeofwavenumbersk. In the domain of microscopic spatial scales comparable to the action range of effective forces of interparticle interaction, the theory reproduces a transition from a regime with typical equilibrium liquid dynamics to a regime with collective particle dynamics where properties similar to solidstate properties appear: effective shear stiffness and transverse (shear) acoustic waves. In the framework of the corresponding approximations, we obtain expressions for the spectral density of transverse particle current for all characteristic regimes in equilibrium collective dynamics. We obtain expressions for the dispersion law for transverse (shear) acoustic waves and also relations for the kinematic shear viscosity ν, the transverse speed of sound v(T), and the corresponding sound damping coefficient Γ(T). We compare the theoretical results with the results of atomistic dynamics simulations of liquid lithium near the melting point

Extended short-range order determines the overall structure of liquid gallium

This journal is © the Owner Societies. Polyvalent metal melts (gallium, tin, bismuth, etc.) have microscopic structural features, which are detected by neutron and X-ray diffraction and which are absent in simple liquids. Based on neutron and X-ray diffraction data and the results of ab initio molecular dynamics simulations for liquid gallium, we examine the structure of this liquid metal at the atomistic level. Time-resolved cluster analysis allows one to reveal that the short-range structural order in liquid gallium is determined by a range of the correlation lengths. This analysis, performed on a set of independent samples corresponding to equilibrium liquid phase, discloses that there are no stable crystalline domains and molecule-like Ga2 dimers typical for crystal phases of gallium. The structure of liquid gallium can be reproduced by the simplified model of the close-packed system of soft quasi-spheres. The results can be applied to analyze the fine structure of other polyvalent liquid metals

Viscous properties of nickel-containing binary metal melts

The paper presents the results of molecular dynamics study of the viscosity of nickel-containing binary metal melts for a wide range of temperatures, including the region of the equilibrium liquid phase and supercooled melt. It is shown that the temperature dependencies of the viscosity of binary metal melts are described by the Kelton’s quasi-universal model. Based on the analysis of the viscosity coefficient of the binary melt composition within the framework of the Rosenfeld’s scale transformations, it has been established that to correctly describe the viscosity of binary/multicomponent metal melts within the framework of entropy models, it is necessary to use a more complex representation of the excess entropy Sex than in the approximation of pair correlation entropy S