arXiv subjects

D. V. Knyazev

Publications and source records attributed to D. V. Knyazev.

7 recordsLinked to original sources

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↗

arXiv2017

Structural, thermodynamic, and transport properties of CH$_2$ plasma in the two-temperature regime

This paper covers calculation of radial distribution functions, specific energy and static electrical conductivity of CH$_2$ plasma in the two-temperature regime. The calculation is based on the quantum molecular dynamics, density functional theory and the Kubo-Greenwood formula. The properties are computed at 5 kK $\le$ $T_i$ $\le$ $T_e$ $\le$ 40 kK and ρ= 0.954 g/cm$^3$ and depend severely on the presence of chemical bonds in the system. Chemical compounds exist at the lowest temperature $T_i$ = $T_e$ = 5 kK considered; they are destroyed rapidly at the growth of $T_i$ and slower at the increase of $T_e$. A significant number of bonds are present in the system at 5 kK $\le$ $T_i$ $\le$ $T_e$ $\le$ 10 kK. The destruction of bonds correlates with the growth of specific energy and static electrical conductivity under these conditions.

physics.plasm-ph↗

arXiv2016

Ab initio calculation of thermodynamic, transport, and optical properties of CH$_2$ plastics

This work covers an ab initio calculation of thermodynamic, transport, and optical properties of plastics of the effective composition CH$_2$ at density 0.954 g/cm$^3$ in the temperature range from 5 kK up to 100 kK. The calculation is based on the quantum molecular dynamics, density functional theory and the Kubo-Greenwood formula. The temperature dependence of the static electrical conductivity $σ(T)$ has a step-like shape: $σ(T)$ grows rapidly for 5 kK <= $T$ <= 10 kK and is almost constant for 20 kK <= $T$ <= 60 kK. The additional analysis based on the investigation of the electron density of states (DOS) is performed. The rapid growth of $σ(T)$ at 5 kK<= $T$ <= 10 kK is connected with the increase of DOS at the electron energy equal to the chemical potential $ε= μ$. The frequency dependence of the dynamic electrical conductivity $σ_1(ω)$ at 5 kK has the distinct non-Drude shape with the peak at $ω\approx 10$ eV. This behavior of $σ_1(ω)$ was explained by the dip at the electron DOS.

cond-mat.mtrl-sci↗

arXiv2014

Transport and optical properties of warm dense aluminum in the two-temperature regime: Ab initio calculation and semiempirical approximation

This work is devoted to the investigation of transport and optical properties of liquid aluminum in the two-temperature case. At first optical properties, static electrical and thermal conductivities were obtained in the \textit{ab initio} calculation. The \textit{ab initio} calculation is based on the quantum molecular dynamics, density functional theory and the Kubo-Greenwood formula. The semiempirical approximation was constructed based on the results of the \textit{ab initio} caculation. The approximation yields the dependences $σ_{1_\mathrm{DC}}\propto1/T_i^{0.25}$ and $K\propto T_e/T_i^{0.25}$ for the static electrical conductivity and thermal conductivity, respectively. The approximation is valid for liquid aluminum at $ρ=2.70$~g/cm$^3$, 3~kK~$\leq T_i\leq T_e\leq20$~kK. Our results are well described by the Drude model with the effective relaxation time $τ\propto T_i^{-0.25}$. We have compared our results with a number of other models. They are all reduced in the low-temperature limit to the Drude model with different expressions for the relaxation time $τ$. Our results are not consistent with the models in which $τ\propto T_i^{-1}$ and support the models which use the expressions with the slower decrease of the relaxation time.

physics.plasm-ph↗

arXiv2013

On the Friedel sum rule in ab initio calculations of optical properties

We investigate the influence of technical parameters in dynamic electrical conductivity calculations by the Kubo-Greenwood formula on the value of the so-called sum rule. We propose a possible explanation of the slight overestimation of the sum rule in most of our results.

physics.comp-ph↗

arXiv2013

Ab initio simulation of complex dielectric function for dense aluminum plasma

We present calculations of frequency-dependent complex dielectric function of dense aluminum plasma by quantum molecular dynamics method for temperatures up to 20 kK. Analysis shows that the dependencies for real and imaginary parts can be interpolated by the Drude formula with two effective parameters: the mean charge of ions and the effective frequency of collisions. The rise of these parameters with temperature deviates from simple theoretical predictions.

cond-mat.mtrl-sci↗

arXiv2013

\textit{Ab initio} calculation of transport and optical properties of aluminum: influence of simulation parameters

This work is devoted to the \textit{ab initio} calculation of transport and optical properties of aluminum. The calculation is based on the quantum molecular dynamics simulation, density functional theory and the Kubo-Greenwood formula. Mainly the calculations are performed for liquid aluminum at near-normal densities for the temperatures from melting up to 20000 K. The results on dynamic electrical conductivity, static electrical conductivity and thermal conductivity are obtained and compared with available reference and experimental data and the calculations of other authors. The influence of the technical parameters on the results is investigated in detail. The error of static electrical conductivity calculation is estimated to be about 20%; more accurate results require bigger number of atoms.

physics.comp-ph↗