arXiv subjects

V. N. Ryzhov

Publications and source records attributed to V. N. Ryzhov.

At least 19 recordsLinked to original sources

arXiv2026

Melting of thin silicon films: a molecular dynamics study with two machine learning potentials

Thermal stability of silicene and thin silicon films is studied by molecular dynamics using two machine-learning potentials, SNAP and GAP. For SNAP potential, systems ranging from a single silicene layer to films of 36 layers are considered. Silicene is found to lose its structure at 500 K. The decomposition temperature increases with film thikness and reaches saturation at about 28 layers, corresponding to the bulk melting point of the SNAP model (1380 K). Thin films up to 8 layers exibit two-phase coexistence upon decomposition, while thicker films undergo surface melting followed by complete collapse into the liquid state. The GAP potential, although more accurate for bulk silicon, fails to describe the gas phase: silicene modelled with GAP decomposes into a set of small clusters. The results are compared with earlier data for the Stillinger-Weber potential.

cond-mat.mtrl-sci↗

arXiv2024

A rare gas mixture: From rigid to gas-like fluid by a mutual concentration change

For a number of mixtures of rate gases at high pressures, sound speed minima are experimentally observed depending on the concentration. This behavior has not yet been explained. We have studied the behavior of a mixture of argon and helium using computer simulation. Sound speed minima have been discovered at a certain concentration, which is in good agreement with experimental data. It is shown that this behavior is due to the fact that the P and T parameters for gas mixtures are near the Frenkel line, separating the states of "rigid" and quasi-gas fluid.

cond-mat.soft↗

arXiv2023

The influence of Gaussian pinning on the melting scenario of a two-dimensional soft-disk system: First-Order versus Continuous Transition

Two-dimensional systems are realized experimentally as thin layers on a substrate. The substrate can have some imperfections (defects of the crystalline structure, chemical impurities, etc.), which demonstrate stronger interaction with the particles of the two-dimensional layer than the rest of the system. Such randomly distributed centers of strong interactions are called "pinning centers". The presence of random pinning can substantially change the behavior of the system. It not only shifts the melting point of the system, but can also change the melting scenario itself. In the present paper the influence of Gaussian pinning on the melting scenario of a two-dimensional system of soft disks is studied by means of molecular dynamics simulation. We randomly introduce into the system of soft disks a set of "pinning centers" which attract the particles via the Gauss potential. We observe that increasing the depth of a Gaussian well leads to a change in the melting scenario of the system. The results demonstrate that simple kind of quenched disorder can significantly affect the melting scenario of two-dimensional systems, offering the possibility of its introduction in complex experiments and studying its influence on the self-assembly and phase diagram of two-dimensional systems in rotating external fields.

cond-mat.soft↗

arXiv2023

Sublimation of silicene and thin silicon films: a view from molecular dynamics simulation

A molecular dynamics simulation of sublimation of silicene and silicon films of different thikness is performed. It is shown that thiner films sublimate at lower temperatures. The sublimation temperature comes to a saturated value of $T=1725$ K at the films thiker than $16$ atomc layers. These results are consistent with the surface mediated collaps of the crystal structure. At the same time this mechanism is different from the crystal structure collapse of graphite and graphene.

cond-mat.mtrl-sci↗

arXiv2022

Molecular simulation of bulk and confined (1,1,1,3,3-pentafluorobutane)

Here we present a computational study of the thermodynamic and structural properties of bulk and confined (1,1,1,3,3-pentafuorobutane) with different lengths of the carbon backbone. The DREIDING force field model has been used in the method of molecular dynamics. In order to study the effect of confinement we have placed (1,1,1,3,3-pentauorobutane) molecules between two graphene walls. In order to study the influence of pore loading on system behavior we have simulated systems of the same size, but with a different number of (1,1,1,3,3-pentauorobutane) molecules, from 200 to 2000. The equations of state at $T = 300$ K in a wide range of densities for all considered systems had a single peculiarity that is attributed to gas-liquid transition. From the two-dimensional radial distribution functions, density profile and angular distribution we have observed the systems split into layers with amorphization rather than crystallization in them.

cond-mat.soft↗

arXiv2021

Anomalous behavior of two-dimensional Hertzian sphere system

The anomalous behavior of a two-dimensional system of Hertzian spheres with exponent $α= 7/2 $ has been studied using the method of molecular dynamics. The phase diagram of this system is the melting line of a triangular crystal with several maxima and minima. Water-like density and diffusion anomalies have been found in the reentrant melting regions. Noteworthy, a density anomaly has been observed not only in the liquid and hexatic but also solid phase. The calculations of the phonon spectra of longitudinal and transverse modes have yielded negative dependence of the frequency of transverse modes on density along all directions in the regions with a density anomaly. This indicates an association of the density anomaly with transverse oscillations of the crystal lattice. The regions of density and diffusion anomalies have been drawn on the phase diagram. It has been found that the stability regions of anomalous diffusion extend to temperatures well above maximum melting point $T = 0.0058$ of the triangular crystal. From analysis of the translational order parameter, which decreases with increasing density in the reentrant melting regions, the presence of a structural anomaly in the system has been assumed.

cond-mat.soft↗

arXiv2021

Glass transition in monatomic systems: smearing of the same structure vs two structure competition

In the present paper we discuss the properties of Voronoi polygons in several monatomic glass-forming systems and compare them with those of the Kob-Andersen mixture. We show that two mechanisms of glass formation are possible: smearing of Voronoi polygons or formation of polygons of two different shapes. Both mechanisms lead to disturbance of the crystalline order in the system and glass transition.

cond-mat.soft↗

arXiv2021

A new mechanism of structural transition in 2D Hertzian spheres in the presence of random pinning

Using molecular dynamics simulation we have investigated the influence of random pinning on the phase diagram and melting scenarios of a two-dimensional (2D) system with the Hertz potential for $α=5/2$. For the first time it has been shown that random pinning can cardinally change the mechanism of first-order transition between the different crystalline phases (triangular and square) by virtue of generating hexatic and tetratic phases: a triangular crystal to hexatic transition is of the continuous Berezinskii-Kosterlitz-Thouless (BKT) type, a hexatic to tetratic transition is of the first-order, and finally, a continuous BKT type transition from tetratic to the square crystal.

cond-mat.soft↗

arXiv2020

The uncertainty of glass transition temperature in molecular dynamics simulations and numerical algorithm for its unique determination

When the cooling rate $v$ is smaller than a certain material-dependent threshold, the glass transition temperature $T_g$ becomes to a certain degree the "material parameter" being nearly independent on the cooling rate. The common method to determine $T_g$ is to extrapolate viscosity $ν$ of the liquid state at temperatures not far above the freezing conditions to lower temperatures where liquid freezes and viscosity is hardly measurable. It is generally accepted that the glass transition occurs when viscosity drops by $13\leq n\leq17$ orders of magnitude. The accuracy of $T_g$ depends on the extrapolation quality. We propose here an algorithm for a unique determining of $T_g$. The idea is to unambiguously extrapolate $ν(T)$ to low temperatures without relying upon a specific model. It can be done using the numerical analytical continuation of $ν(T)$-function from above $T_g$ where it is measurable, to $T\gtrsim T_g$. For numerical analytical continuation, we use the Pade approximant method.

physics.chem-ph↗

arXiv2020

Freezing of two-length-scale systems: complexity, universality and prediction

Two-length-scale pair potentials arise ubiquitously in condensed matter theory as effective interparticle interactions in molecular, metallic and soft matter systems. The existence of two different bond lengths generated by the shape of potential causes complex behavior in even one-component systems: polymorphism in solid and liquid states, water-like anomalies, the formation of quasicrystals and high stability against crystallization. Here we address general properties of freezing in one-component two-length-scale systems and argue that the formation of solid phases during cooling a liquid is essentially determined by the radial distribution function (RDF) of the liquid. We show that different two-length-scale systems having similar RDF freeze into the same solid phases. In most cases, the similarity between RDFs can be expressed by the proximity of two dimensionless effective parameters: the ratio between effective bond lengths, $λ$, and the fraction of short-bonded particles $ϕ$. We validate this idea by studying the formation of different solid phases in different two-length-scale systems. The method proposed allows predicting effectively the formation of solid phases in both numerical simulations and self-assembling experiments in soft matter systems with tunable interactions.

physics.chem-ph↗

arXiv2020

Crystal structures of a core-softened system confined in a narrow slit pore

We investigate a behavior of a core-softened system in a thin slit pore (the width of the pore is equil to three diameters of the particles). In previous studies it was shown that strongly confined systems form crystalline phases which consist of several triangular or square layers. These phases can be also considered as cuts of FCC or HCP structures. We show that the behavior of the core-softened system is more complex. We observe also a quasicrystalline phase. Moreover, the phase with two triangular layers appears at lower densities than the one with two square layers which is in contrast to the behavior of the systems studied before. These results demonstrate that the phase behavior of strongly confined systems can be even more complex than it was supposed before.

cond-mat.soft↗

arXiv2019

Melting scenarios of two-dimensional Hertzian spheres with a single triangular lattice

We present a molecular dynamics simulation study of the phase diagram and melting scenarios of two-dimensional Hertzian spheres with exponent 7/2. We have found multiple re-entrant melting of a single crystal with a triangular lattice in a wide range of densities from 0.5 to 10.0. Depending on the position on the phase diagram, the triangular crystal has been shown to melt through both two-stage melting with a first-order hexatic - isotropic liquid transition and a continuous solid - hexatic transition as well as in accordance with the Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young (BKTHNY) scenario (two continuous transitions with an intermediate hexatic phase). We studied the behavior of heat capacity and have shown that despite two-stage melting, the heat capacity has one peak which seems to correspond to a solid-hexatic transition.

cond-mat.soft↗

arXiv2019

Interplay between freezing and density anomaly in a confined core-softened system

We present a computer simulation study of influence of the confinement on the density anomaly in the system with isotropic core-softened potential which is used for a qualitative description of the anomalous behavior of water and some other liquids. We have found that a maximum temperature of the density anomaly region along an isochor $ρ=0.5$ does not depend on the pore width. We have shown that a decrease in the width of the confining slit pore leads to an increase in the crystallization temperature and as a result the local density distribution is mostly controlled by the particle-wall interaction, which leads to the depression of the density anomaly.

cond-mat.soft↗

arXiv2019

The effect of confinement on the solid-liquid transition in a core-softened potential system

We present a comparative computer simulation study of the phase diagrams and anomalous behavior of two-dimensional ($2D$) and quasi-two-dimensional ($q2D$) classical particles interacting with each other through isotropic core-softened potential which is used for a qualitative description of the anomalous behavior of water and some other liquids. We have shown that at the low density part of the phase diagram an increase in the width of the confining slit pore leads to a considerable decrease in the melting temperature while at high densities the melting temperature is almost unchanged.

cond-mat.soft↗

arXiv2019

The influence of random pinning on the melting scenario of two-dimensional soft-disk systems

We present the results of a computer simulation study of the melting scenario of two-dimensional soft-disk systems with potential $U(r)=\varepsilon(σ/r)^n$, $n=12$ and $n=1024$, both in the presence of random pinning and without it. The melting parameters have been determined from analysis of the behavior of equations of state, correlation functions of the orientational and translational order parameters, Young modulus and renormalization group equations. The transition points obtained from these criteria are in good agreement. We have shown that the systems melted in two stages - first-order hexatic phase to liquid transition and the continuous Berezinskii-Kosterlitz-Thouless type crystal-hexatic phase transition. Random pinning widened the hexatic phase, but left the melting scenario unchanged.

cond-mat.soft↗

arXiv2019

Anomalous behavior of dispersion of longitudinal and transverse collective excitations in water

We study the dependence of the excitation frequency of water along an isochore and an isotherm crossing the region of density anomaly. We have shown that the frequency of the longitudinal excitations demonstrated anomalous dependence on temperature along the isochore. At the same time the dependence for both longitudinal and transverse excitation frequencies on density along the isotherm are very modest or even negligible in rather wide range of densities. This kind of behavior also seems anomalous in comparison with the ordinary liquids.

cond-mat.soft↗

arXiv2019

Two dimensional vortex structures with multi scale interactions in thin film superconductors

Interaction of particles of many systems can be effectively approximated by multiscale interaction potentials. Such potentials are widely used for investigation of colloidal systems and colloid-polymer mixtures, complex liquids (for instance, water) and other system. Also, it is of particular interest that effective interaction of vortices in a thin superconducting film can be approximated by a multiscale potential. The subject matter of the present paper is a system like this. Based on a multiscale potential we have shown that this system demonstrated a large number of different phases. It is particularly important that we analyze the influence of a long-range interaction of the system properties and show that properly taking into account long-range forces results in a dramatic change in the system phase diagram.

cond-mat.soft↗

arXiv2019

Possible phase transition in liquid Cesium at ambient pressure

We report a molecular dynamics study of liquid cesium at ambient pressure intended to check the possibility of liquid-liquid phase transformation at $T=590$ K. We find the presence of small kinks on thermodynamic characteristics of the system, but no phase transition.

cond-mat.soft↗