Local structural features of metallic alloys: Ni<inf>33</inf>Zr<inf>67</inf> and Ni<inf>50</inf>Zr<inf>50</inf>

In this work we present the results of computer simulations molecular dynamics of the metallic alloys: Ni33Zr67 and Ni50Zr50. The critical glass-forming temperatures are defined from the behavior change of theWendt-Abraham parameters of the studied systems. We have found that the increase in the concentration of nickel in the system NiZr leads to displacement of the critical glass-forming temperature in higher temperature region. It is shown that the structural transformations which were observed in the Ni50Zr50 system are not related with crystallization processes

Dynamics of a network of hydrogen bonds upon water electrocrystallization

Computer simulation is employed to study the dynamics of a network of hydrogen bonds and the structural properties of water placed between graphene layers. The presence of the graphene walls has been shown to substantially affect the water phase diagram. Glass transition processes are observed in the system, and liquid water completely passes to an amorphous state. Moreover, it has been established that the imposition of an external electric field with strength E ≥ 0.5 V/Å on the system subjected to increased pressure results in structural ordering of water. It has been found that water located between graphene layers is transformed into Ic cubic ice. The electrocrystallization of water has been shown to substantially change the dynamics of the network of hydrogen bonds. © 2013 Pleiades Publishing, Ltd

Structural and dynamic features of water and amorphous ice

© 2017, Pleiades Publishing, Ltd.Structural properties and microscopic dynamics of water and amorphous ice have been studied by the molecular dynamics method. It has been found that the distribution function of the tetrahedricity parameter exhibits two ranges, which correspond to local molecular formations with low and high degrees of tetrahedricity. The number of molecular clusters with a high degree of tetrahedricity grows as temperature decreases. It has been shown that the vibrational density of states comprises two vibrational modes. A low-frequency vibrational mode strongly depends on pressure and is almost independent of temperature, while a high-frequency mode is relevant to the pressure-independent heat motion of molecules. The geometric criterion of hydrogen bonds has been used to evaluate their continuous lifetime as depending on temperature for molecules with different coordination values. The average lifetime of a hydrogen bond substantially depends on the coordination of molecules, with the temperature dependence of the coordination obeying the activation dynamics

Microscopic collective dynamics of water

© 2016, Pleiades Publishing, Ltd.Data obtained on microscopic collective excitations in water by molecular dynamics simulation within the framework of the coarse-grained mW-model of the intermolecular interaction potential for water are reported. The calculated spectra of the dynamic structure factor and spectral densities of time correlation functions of longitudinal and transverse currents reveal the existence of propagating collective excitations of longitudinal and transverse polarization in water for a wide range of wavenumbers. The dynamics of fluctuations in the particle number density is analyzed within the framework of a microscopic theory that takes into account only the structural features of a system. The theoretically calculated data on the spectra of dynamic structure factor in a wavenumber range of 0.13–0.48 Å–1 are in good agreement with the results of molecular dynamics simulation

Atomic collective excitations in liquid lead

© 2014, Pleiades Publishing, Inc. The atomic dynamics of liquid lead at the temperature T = 600 K has been simulated on the basis of the embedded atom model potential (the “embedded” atom model making it possible to effectively take into account the many-particle interactions) in order to study the mechanisms of formation of the atomic collective excitations. Spectra of the dynamic structure factor S(k, ω) and the spectral densities of the time correlation functions of the longitudinal (formula presented.) (k, ω) and transverse (formula presented.) (k, ω) currents have been calculated for the wavenumber region 0.11 Å−1 ≤ k ≤ 2.01 Å−1. It has been established that the dynamics of density fluctuations is characterized by two dispersion “acoustic-like” branches of the longitudinal and transverse polarization

Short-range structural transformations in water at high pressures

We report results of molecular dynamics simulations of liquid water at the temperature T = 277 K for a range of high pressure. One aim of the study was to test the model Amoeba potential for the description of equilibrium structural properties and dynamical processes in liquid water. In comparing our numerical results with the Amoeba and TIP5P potentials, our results of ab initio molecular dynamics simulations and the experimental data reveal that the Amoeba potential reproduces correctly structural properties of the liquid water. Another aim of our work was related with the investigation of the pressure induced structural transformations and their influence on the microscopic collective dynamics. We have found that the structural anomaly at the pressure pc ≈ 2000 Atm is related with the changes of the local, short-range order in liquid water within the first two coordination shells. This anomaly specifies mainly by deformation of the hydrogen-bond network. We also discuss in detail the anomalous behavior of sound propagation in liquid water at high pressures and compare numerical results with the experimental data. © 2011 Elsevier B.V. All rights reserved

Local structural order and single-particle dynamics in metallic glass

The atomic dynamics of the amorphous metallic alloy Al50Cu 50 is investigated in this work. The critical glass-forming temperature is defined from the behavior change of the Wendt-Abraham parameter and the pair-correlation entropy, and is Tc ≈ 500 K. It is shown that the power-fractional memory function allows us to describe in the framework of the mode-coupling theory the time dependences of the incoherent scattering functions obtained from the atomic dynamic simulations for the wide region of temperatures (T = 100-2000 K). © Allerton Press, Inc., 2010

Dynamic heterogeneity of a colloidal solution near the sol-gel transition

The results of the simulation of the dynamics of particles in a colloidal solution in the vicinity of the sol-gel transition are presented. The Van Hove correlation function, incoherent scattering function, and mean-square displacement of particles at different temperatures and volume densities have been calculated from the simulation data. The effects of dynamic heterogeneity have been evaluated numerically and the gelation temperature at different volume densities has been determined using the non-Gaussian parameter. It has been shown that the specific features observed in the dynamics of particles in the colloidal solution near the sol-gel transition are explained by the conventional separation of the particles in the system into fast particles, which contribute to translational diffusion, and slow particles, which participate predominantly in vibrational processes. © 2011 Pleiades Publishing, Ltd

Vibrational features of water at the low-density/high-density liquid structural transformations

A structural transformation in water upon compression was recently observed at the temperature T=277K in the vicinity of the pressure p≈2000atm [R.M. Khusnutdinoff, A.V. Mokshin, J. Non-Cryst. Solids 357 (2011) 1677]. It was found that the transformations are related with the principal structural changes within the first two coordination shells as well as the deformation of the hydrogen-bond network. In this work, we study in detail the influence of these structural transformations on the vibrational molecular dynamics of water by means of molecular dynamics simulations on the basis of the model Amoeba potential (T=290K, p=1.0÷10000atm). The equation of state and the isothermal compressibility are found for the considered (p, T)-range. The vibrational density of states extracted for THz-frequency range manifests two distinct modes, where the high-frequency mode is independent of pressure whereas the low-frequency one has the strong, non-monotonic pressure-dependence and exhibits a step-like behavior at the pressure p≈2000atm. The extended analysis of the local structural and vibrational properties discovers that there is a strong correlation between the primary structural and vibrational aspects of the liquidliquid structural transformation related with the molecular rearrangement within the range of the second coordination shell. © 2012 Elsevier B.V. All rights reserved