arXiv subjects

E. N. Tsiok

Publications and source records attributed to E. N. Tsiok.

At least 37 records · Page 2Linked to original sources

arXiv2018

Phase diagram and melting scenarios of two-dimensional Hertzian spheres

We present computer simulations of a system of purely repulsive soft colloidal particles interacting via the Hertz potential and constrained to a two-dimensional plane. This potential describes the elastic interaction of weakly deformable bodies and can be a reliable model for qualitative description of behavior of soft macromolecules, like globular micelles and star polymers. We find a large number of ordered phases, including the dodecagonal quasicrystal, and analyze the melting scenarios of low density triangle and square phases. It is interesting that depending on the position on the phase diagram the system can melt both through the first order transition and in accordance with the Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young (BKTHNY) scenario (two continuous transitions with the intermediate hexatic phase) and also in accordance with recently proposed two-stage melting with the first order hexatic-isotropic liquid transition and continuous solid-hexatic transition. We also demonstrate the possibility of the tricritical point on the melting line.

cond-mat.soft↗

arXiv2017

Complex crystalline structures in a two-dimensional core-softened system

A cascade of phase transitions from square to hexagonal lattice is studied in 2D system of particles interacting via core-softened potential. Due to the presence of two length-scales of repulsion, different local configurations with four, five, and six neighbors enable, leading to formation of complex crystals. The previously proposed interpolation method is generalized for calculation of pair correlations in crystals which elemental cell consists of more than one particle. A high efficiency of the method is illustrated using a snub square lattice as a representative example. Using molecular dynamics simulations, it is found that the snub square lattice is being broken under heating, generating high density quasicrystalline phase with 12-fold symmetry. Simple theoretical model is proposed to explain the physical mechanism governing this phenomenon: With density growth (from square to hexagonal phases), the concentrations of different local configurations randomly realized through plane tilling are being changed that minimizes the energy of the system. The calculated phase diagram in the intermediate region of densities justifies the existence of HD12 phase and demonstrates a cascade of the first-order transitions "square -- HD12 -- hexagonal" solid phases with the density growth. The results allow us to better understand the physical mechanisms responsive for formation of quasicrystals, and, therefore, should be of interest for broad community on material science and soft matter.

cond-mat.soft↗

arXiv2017

A novel anomalous region of water

Water is the most important liquid in the Universe. At the same time it is the most anomalous liquid. It demonstrates several dozens of anomalies, among which are density anomaly, diffusion anomaly etc. Anomalous behavior of water is a topic numerous publications. However, most of the publications investigate the anomalous behavior of water in the vicinity of critical points: the liquid-gas critical point and the second hypothetical critical point in supercooled region. Here we analyze experimental data on such properties of water as heat capacity, speed of sound, dynamic viscosity and thermal conductivity. We show that these properties demonstrate anomalous maxima and minima in a region which is far from both critical points. Therefore, we find a novel region of anomalous properties of water (anomalous triangle) which cannot be related to critical fluctuations. We also perform a molecular dynamics simulations of this region with two common water models - SPC/E and TIP4P - and show that these models fail to describe the novel anomalous region.

cond-mat.soft↗

arXiv2017

Random pinning elucidates the nature of melting transition in two-dimensional core-softened potential system

Despite about forty years of investigations, the nature of the melting transition in two dimensions is not completely clear. In the framework of the most popular Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young (BKTHNY) theory, 2D systems melt through two continuous Berezinskii-Kosterlitz-Thouless (BKT) transitions with intermediate hexatic phase. The conventional first-order transition is also possible. On the other hand, recently on the basis of computer simulations the new melting scenario was proposed with continuous BKT type solid-hexatic transition and first order hexatic-liquid transition. However, in the simulations the hexatic phase is extremely narrow that makes its study difficult. In the present paper, we propose to apply the random pinning to investigate the hexatic phase in more detail. The results of molecular dynamics simulations of two dimensional system having core-softened potentials with narrow repulsive step which is similar to the soft disk system are outlined. The system has a small fraction of pinned particles giving quenched disorder. Random pinning widens the hexatic phase without changing the melting scenario and gives the possibility to study the behavior of the diffusivity and order parameters in the vicinity of the melting transition and inside the hexatic phase.

cond-mat.soft↗

arXiv2016

Influence of random pinning on melting scenario of two-dimensional core-softened potential system

The random disorder can drastically change the melting scenario of two-dimensional systems and has to be taken into account in the interpretation of the experimental results. We present the results of the molecular dynamics simulations of the two dimensional system with the core-softened potentials with two repulsive steps in which a small fraction of the particles is pinned, inducing quenched disorder. It is shown that without the quenched disorder the system with small repulsive shoulder, which is close in the shape to the soft disks, melts in accordance with the melting scenario proposed in Refs. [30,31,33] (first-order liquid-hexatic and continuous hexatic-solid transitions). Random pinning widens the hexatic phase, but leaves the melting scenario unchanged. For the system with larger repulsive step at high densities the conventional first-order transition takes place without random pinning. However, in the presence of disorder the single first-order transition transforms into two transitions, one of them (solid-hexatic) is the continuous KTHNY-like transition, while the hexatic to isotropic liquid transition occurs as the first order transition.

cond-mat.soft↗

arXiv2015

Can random pinning change the melting scenario of two-dimensional core-softened potential system?

In experiments the two-dimensional systems are realized mainly on solid substrates which introduce quenched disorder due to some inherent defects. The defects of substrates influence the melting scenario of the systems and have to be taken into account in the interpretation of the experimental results. We present the results of the molecular dynamics simulations of the two dimensional system with the core-softened potential in which a small fraction of the particles is pinned, inducing quenched disorder.The potentials of this type are widely used for the qualitative description of the systems with the water-like anomalies. In our previous publications it was shown that the system demonstrates an anomalous melting scenario: at low densities the system melts through two continuous transition in accordance with the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) theory with the intermediate hexatic phase, while at high densities the conventional first order melting transition takes place. We find that the well-known disorder-induced widening of the hexatic phase occurs at low densities, while at high density part of the phase diagram random pinning transforms the first-order melting into two transitions: the continuous KTHNY-like solid-hexatic transition and first-order hexatic-isotropic liquid transition.

cond-mat.soft↗

arXiv2015

Water in Asbestos

We present the molecular simulation study of the behavior of water and sodium chloride solution confined in lizardite asbestos nanotube which is a typical example of hydrophilic confinement. The local structure, orientational and dynamic properties are studied. It is shown that the diffusion coefficient drops about two orders of magnitude comparing to the bulk case, and water in lizardite asbestos tubes experiences vitrification rather then crystallization upon cooling in accordance with the results for some other hydrophilic confinements. The behavior of sodium chloride solutions also considered and the formation of double layer is observed. It is shower that both sodium and chlorine have larger diffusion coefficients then water.

physics.chem-ph↗

arXiv2015

Direct evidence for strong crossover of collective excitations and positive sound dispersion in the supercritical state

Supercritical state has been viewed as an intermediate state between gases and liquids with largely unknown physical properties. Here, we address the important ability of supercritical fluids to sustain collective excitations. We directly study propagating modes on the basis of correlation functions calculated from extensive molecular dynamics simulations, and find that the supercritical system sustains propagating solid-like transverse modes below the Frenkel line but becomes devoid of transverse modes above the line where it supports longitudinal modes only. Important thermodynamic implications of this finding are discussed. We directly detect positive sound dispersion (PSD) below the Frenkel line where transverse modes are operative, quantitatively explain its magnitude on the basis of transverse and longitudinal velocities. PSD disappears above the Frenkel line which therefore demarcates the supercritical phase diagram into two areas where PSD does and does not operate.

cond-mat.stat-mech↗

arXiv2015

The Behavior of Cyclohexane Confined in Slit Carbon Nanopore

It is well known that confining a liquid into a pore strongly alters the liquid behavior. Investigations of the effect of confinement are of great importance for many scientific and technological applications. Here we present a molecular dynamics study of the behavior of cyclohexane confined in carbon slit pores. The local structure and orientational ordering of cyclohexane molecules are investigated. It is shown that the system freezes with decreasing the pore width, and the freezing temperature of nanoconfined cyclohenae is higher than the bulk one.

cond-mat.soft↗

arXiv2015

Dynamical Crossover in Supercritical Core-Softened Fluids

It is well known that some liquids can demonstrate anomalous behavior. Interestingly, this be- havior can be qualitatively reproduced with simple core-softened isotropic pair-potential systems. Although anomalous properties of liquids usually take place at low and moderate temperatures it was recently recognized that many important phenomena can appear in supercritical fuids. However, no studies of supercritical behavior of core-softened fuids is reported. This paper reports a study of dynamical crossover in supercritical core-softened systems. The crossover line is calculated from three different criteria and good agreement between them is observed. It is found that the behavior of the dynamical crossover line of core-softened systems is quite complex due to its quasi-binary nature.

cond-mat.stat-mech↗

arXiv2015

Dynamical Crossover in Supercritical Water

Dynamical crossover in water is studied by means of computer simulation. The crossover temperature is calculated from the behavior of velocity autocorrelation functions. The results are compared with experimental data. It is shown that the qualitative behavior of the dynamical crossover line is similar to the melting curve behavior. Importantly, the crossover line belongs to experimentally achievable $(P,T)$ region which stimulates the experimental investigation in this field.

cond-mat.soft↗

arXiv2014

Phase diagram of the system with the repulsive shoulder potential in two dimensions: density functional approach

In the framework of the density functional theory of freezing proposed in our previous works, we calculate the phase diagram of two-dimensional system of particles interacting through the repulsive shoulder potential. This potential consists of the hard core and repulsive shoulder of the larger radius. It is shown that at low densities the system melts through the continuous transition in accordance with the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario, while at high densities the conventional first order transition takes place.

cond-mat.stat-mech↗

arXiv2014

Thermodynamics and Widom lines in supercritical carbon dioxide

Behavior of supercritical fluids attracts a lot of attention nowadays. It is important both from the point of view of fundamental science and technological applications. However, up to now the progress in the field is rather moderate. In this article we report a computational study of supercritical carbon dioxide which is one of the most important fluids for chemical industry. We study the response functions of $CO_2$ in supercritical regime and calculate the locations of their maxima (Widom lines). We also make preliminary calculations of the line of crossover of microscopic dynamics of particles (Frenkel line). The conclusions on the Frenkel line location can be applied to study of the atmosphere of Venus.

cond-mat.stat-mech↗

arXiv2014

The Behavior of Benzene Confined in Single Wall Carbon Nanotube

We present the molecular dynamics study of benzene molecules confined into the single wall carbon nanotube. The local structure and orientational ordering of benzene molecules are investigated. It is found that the molecules mostly group in the middle distance from the axe of the tube to the wall. The molecules located in the vicinity of the wall demonstrate some deviation from planar shape. There is a tilted orientational ordering of the molecules which depends on the location of the molecule. It is shown that the diffusion coefficient of the benzene molecules is very small at the conditions we report here.

cond-mat.mes-hall↗

arXiv2014

Anomalous Melting Scenario of the Two-Dimensional Core-Softened System

We consider the phase behavior of two-dimensional ($2D$)system of particles with an isotropic core-softened potential introduced in our previous publications. As one can expect from the qualitative consideration for the three dimensional case, the system demonstrates a reentrant-melting transition at low densities along with waterlike anomalies in the fluid phase near the melting maximum. In contrast with the three dimensional case, in two dimensions melting is a continuous two-stage transition in the low density part of the phase diagram with an intermediate hexatic phase corresponding to the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario. At the same time, at high densities the system melts through one first-order transition. We also show, that the order of the region of anomalous diffusion and the regions of density and structural anomalies are inverted in comparison with the $3D$ case and have silicalike sequence.

cond-mat.soft↗

arXiv2014

Effect of a potential softness on the solid-liquid transition in a two-dimensional core-softened potential system

In the present paper, using a molecular dynamics simulation, we study a nature of melting of a two-dimensional ($2D$) system of classical particles interacting through a purely repulsive isotropic core-softened potential which is used for the qualitative description of the anomalous behavior of water and some other liquids. We show that the melting scenario drastically depends on the potential softness and changes with increasing the width of the smooth repulsive shoulder. While at small width of the repulsive shoulder the melting transition exhibits what appears to be weakly first-order behavior, at larger values of the width a reentrant-melting transition occurs upon compression for not too high pressures, and in the low density part of the $2D$ phase diagram melting is a continuous two-stage transition, with an intermediate hexatic phase in accordance with the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario. On the other hand, at high density part of the phase diagram one first-order transition takes place. These results may be useful for the qualitative understanding the behavior of water confined between two hydrophobic plates.

cond-mat.soft↗

arXiv2014

How to quantify structural anomalies in fluids?

Some fluids are known to behave anomalously. The so-called structural anomaly which means that the fluid becomes less structures under isothermal compression is among the most frequently discussed ones. Several methods for quantifying the degree of structural order are described in the literature and are used for calculating the regions of structural anomalies. It is implied that all of the structural order determinations yield qualitatively identical results. However, no explicit comparison was made. This paper presents such a comparison for the first time. the results of some definitions are shown to contradict the intuitive notion of a fluid. On the basis of this comparison we show that the structural anomaly can be most reliably determined from the behavior of the excess entropy.

cond-mat.soft↗

arXiv2014

Dynamic transition in supercritical iron

Recent advance in understanding the supercritical state posits the existence of a new line above the critical point separating two physically distinct states of matter: rigid liquid and non-rigid gas-like fluid. The location of this line, the Frenkel line, remains unknown for important real systems. Here, we map the Frenkel line on the phase diagram of supercritical iron using molecular dynamics simulations. On the basis of our data, we propose a general recipe to locate the Frenkel line for any system, the recipe that importantly does not involve system-specific detailed calculations and relies on the knowledge of the melting line only. We further discuss the relationship between the Frenkel line and the metal-insulator transition in supercritical liquid metals. Our results enable predicting the state of supercritical iron in several conditions of interest. In particular, we predict that liquid iron in the Jupiter core is in the "rigid liquid" state and is highly conducting. We finally analyse the evolution of iron conductivity in the core of smaller planets such as Earth and Venus as well as exoplanets: as planets cool off, the supercritical core undergoes the transition to the rigid-liquid conducting state at the Frenkel line.

cond-mat.stat-mech↗