arXiv subjects

G. S. Demyanov

Publications and source records attributed to G. S. Demyanov.

10 recordsLinked to original sources

arXiv2026

Mechanical properties of V-4Ti-4Cr alloy from molecular dynamics with a neural-network potential

Machine-learning interatomic potentials enable large-scale atomistic simulations of vanadium alloys relevant to fusion applications, but reliable training and validation remain challenging in multicomponent systems. Here, we develop a descriptor-based DeepMD-DPA1 potential for the V-Ti-Cr system using a two-stage workflow: broad configuration sampling driven by the MatterSim foundation model followed by fine-tuning to density-functional-theory data computed with VASP. The model achieves root-mean-square errors of 9.2 meV/atom for energies and 0.23 eV/angstrom for force components. Using this potential in large-cell LAMMPS simulations, we compute Young's modulus, bulk modulus, and Poisson's ratio for V-4Ti-xCr and V-xTi-4Cr alloys at T = 300 K and T = 1073 K. We find that increasing Cr fraction increases the elastic moduli of the alloy, while increasing Ti fraction decreases them; all compositions are softer at 1073 K than at 300 K. Two-phase simulations give a melting temperature for pure V of 1950 K, in good agreement with experimental data.

cond-mat.mtrl-sci↗

arXiv2026

A wide-range temperature-dependent deep potential for sodium with near-experimental accuracy from melting to the critical point

We construct temperature-dependent deep potentials for sodium using finite-temperature DFT data obtained with the PBE, AM05, and $r^2$SCAN exchange-correlation functionals and investigate the thermophysical properties of sodium from room temperature to the critical region. The predicted critical parameters show a dependence on the exchange-correlation functional. The model based on the $r^2$SCAN functional gives a critical temperature $T_c=2.508(8)$ kK, density $ρ_c=0.203(4)$ g/cm$^{3}$, and pressure $P_c=0.249(6)$ kbar, in close agreement with the recommended values. This model is then used to reconstruct the normal-pressure and critical isobars and to calculate the enthalpy, heat capacities, thermal expansion coefficient, bulk moduli, Grüneisen parameter, and speed of sound. The calculated normal-pressure bcc density differs by only 0.06% from the experimental value. Direct solid-liquid coexistence simulations give a melting temperature of $346(2)$ K, 25 K below the recommended value, consistent with the sensitivity expected from meV/atom free-energy errors. Liquid-vapor coexistence simulations reproduce the binodal and yield a surface tension that approaches zero near the critical point. The calculated self-diffusion coefficient and shear viscosity extend the available transport-property data into the expanded-liquid and near-critical regions, where direct experimental information is sparse. We also demonstrate the thermodynamic consistency of the results by comparing the speed of sound obtained from direct acoustic simulations with that calculated from the equation of state.

physics.comp-ph↗

arXiv2025

One--Component Plasma Equation of State Revisited via Angular--Averaged Ewald Potential

We present analytic fits of classical one--component plasma (OCP) internal energy over a wide range of coupling parameter $0.01\leΓ\le 170$ using Monte--Carlo data in the thermodynamic limit. We extend the dataset obtained in [Demyanov and Levashov, Phys. Rev. E 106, 015204 (2022)] using the angular--averaged Ewald potential with additional points at strong coupling ($Γ=120,\ 150,\ 170$). We then fit two frequently used functional forms for the OCP equation of state: (i) a five-parameter equation by Caillol [J. Chem. Phys. 111, 6538--6547 (1999)] and (ii) the equation by Potekhin and Chabrier [Phys. Rev. E 62, 8554 (2000)] that enforces the Debye--Hückel limit. The presented fits reproduce our MC data within statistical uncertainties, recovering the correct weak-coupling behavior. Coefficients, recommended validity ranges, and comparisons to prior analytical and simulation results are provided.

physics.plasm-ph↗

arXiv2025

Molecular dynamics of nondegenerate hydrogen plasma using improved Kelbg pseudopotential with electron finite-size correction

This paper is devoted to semiclassical molecular dynamics simulation of nondegenerate hydrogen plasma using an improved Kelbg pseudopotential. The main novelty of our method is accounting for the finite size of electrons. This modification resolves the nonphysical cluster formation at temperatures below 50 kK, which was first reported by A.V. Filinov [Phys. Rev. E 70, 046411 (2004)]. However, the energy still appears to be underestimated at low temperatures, as indicated by comparisons with the recent path integral Monte Carlo calculations [Phys. Plasmas 31, 110501 (2024)]. Using the presented method, we analyze the dependence of radial distribution functions, composition, ionization degree, energy, and pressure on the plasma coupling parameter, while maintaining a fixed degeneracy parameter. Additionally, we demonstrate the impact of incorporating long-range interactions on the energy $N$-dependence by utilizing the angular-averaged Ewald potential. Finally, we compute the thermodynamic limits for energy and pressure.

physics.plasm-ph↗

arXiv2023

Stability of a Nondegenerate Two--Component Weakly Coupled Plasma

The paper discusses the problem of stability of a two-component plasma and proposes a consistent consideration of quantum and long-range effects to calculate the thermodynamic properties of such a plasma. We restrict ourselves by the case of a non-degenerate plasma to avoid the fermionic sign problem and consider the weakly coupled regime. Long-range interaction effects are taken into account using the angular-averaged Ewald potential (AAEP). To calculate thermodynamic properties, we apply both classical Monte Carlo (CMC) and path integral Monte Carlo (PIMC) methods. A special method is developed to correctly calculate potential energy in PIMC simulations with long-range interaction effects. Our theoretical estimations show that the probability of a bound state formation is very low at a coupling parameter $Γ~\le~0.01$, so both classical and quantum simulations give the same energy at $Γ~\leq~0.01$, and the thermodynamic limit coincides with the Debye--Hückel theory. At higher $Γ$, the $N$-convergence is lost due to the formation of bound states.

physics.plasm-ph↗

arXiv2023

Pressure of Coulomb systems with volume-dependent long-range potentials

In this work, we consider the pressure of Coulomb systems, in which particles interact via a volume-dependent potential (in particular, the Ewald potential). We confirm that the expression for virial pressure should be corrected in this case. We show that the corrected virial pressure coincides with the formula obtained by differentiation of free energy if the potential energy is a homogeneous function of particle coordinates and a cell length. As a consequence, we find out that the expression for pressure in the recent paper by J. Liang \textit{et al.} [\href{https://doi.org/10.1063/5.0107140}{J. Chem. Phys. \textbf{157}, 144102 (2022)}] is incorrect.

physics.comp-ph↗

arXiv2022

One--Component Plasma of a Million Particles via angular--averaged Ewald potential: A Monte Carlo study

In this work, we derive a correct expression for the one--component plasma (OCP) energy via the angular--averaged Ewald potential (AAEP). Unlike E.~Yakub and C.~Ronchi (J. Low Temp. Phys. 139, 633 (2005)), who had tried to obtain the same energy expression from a two--component plasma model, we used the original Ewald potential for an OCP. A constant in the AAEP was determined using the cluster expansion in the limit of weak coupling. The potential has a simple form suitable for effective numerical simulations. To demonstrate the advantages of the AAEP, we performed a number of Monte--Carlo simulations for an OCP with up to a million particles in a wide range of the coupling parameter. Our computations turned out at least two orders of magnitude more effective than those with a traditional Ewald potential. A unified approach is offered for the determination of the thermodynamic limit in the whole investigated range. Our results are in good agreement with both theoretical data for a weakly coupled OCP and previous numerical simulations. We hope that the AAEP will be useful in path integral Monte Carlo simulations of the uniform electron gas.

physics.plasm-ph↗

arXiv2022

Systematic derivation of angular--averaged Ewald potential

In this work we provide a step by step derivation of an angular--averaged Ewald potential suitable for numerical simulations of disordered Coulomb systems. The potential was first introduced by E.\,Yakub and C.\,Ronchi without a clear derivation. Two methods are used to find the coefficients of the series expansion of the potential: based on the Euler--Maclaurin and Poisson summation formulas. The expressions for each coefficient is represented as a finite series containing derivatives of Jacobi theta functions. We also demonstrate the formal equivalence of the Poisson and Euler--Maclaurin summation formulas in the three-dimensional case. The effectiveness of the angular--averaged Ewald potential is shown by the example of calculating the Madelung constant for a number of crystal lattices.

physics.plasm-ph↗

arXiv2022

Derivation of the Kelbg potential/functional

The density matrix for a system of particles interacting via the Coulomb potential is obtained in the high--temperature limit following almost entirely the original work by Kelbg. For this purpose the Blöch equation is solved in the first order of perturbation theory. We tried to explain all the transformations in the derivation in order to simplify the understanding of this non-trivial theory. The solution of Kelbg is widely used in path integral simulations of Coulomb systems.

physics.plasm-ph↗

arXiv2021

Ab initio inspection of thermophysical experiments for zirconium near melting

We present quantum molecular dynamics calculations of thermophysical properties of solid and liquid zirconium in the vicinity of melting. An overview of available experimental data is also presented. We focus on the analysis of thermal expansion, molar enthalpy, resistivity and normal spectral emissivity of solid and liquid Zr. Possible reasons of discrepancies between the first-principle simulations and experiments are discussed. Our calculations reveal a significant volume change on melting in agreement with electrostatic levitation experiments. Meanwhile, we confirm a low value of enthalpy of fusion obtained in some pulse-heating experiments. Electrical resistivity of solid and liquid Zr is systematically underestimated in our simulations, however the slope of resistivity temperature dependencies agrees with experiment. Our calculations predict almost constant normal spectral emissivity in liquid Zr.

cond-mat.mtrl-sci↗