15 research outputs found
Thermodynamics of hot dense H-plasmas: Path integral Monte Carlo simulations and analytical approximations
This work is devoted to the thermodynamics of high-temperature dense hydrogen
plasmas in the pressure region between and Mbar. In particular
we present for this region results of extensive calculations based on a
recently developed path integral Monte Carlo scheme (direct PIMC). This method
allows for a correct treatment of the thermodynamic properties of hot dense
Coulomb systems. Calculations were performed in a broad region of the
nonideality parameter and degeneracy parameter . We give a comparison with a few available results from
other path integral calculations (restricted PIMC) and with analytical
calculations based on Pade approximations for strongly ionized plasmas. Good
agreement between the results obtained from the three independent methods is
found.Comment: RevTex file, 21 pages, 5 ps-figures include
Wigner function quantum molecular dynamics
Classical molecular dynamics (MD) is a well established and powerful tool in
various fields of science, e.g. chemistry, plasma physics, cluster physics and
condensed matter physics. Objects of investigation are few-body systems and
many-body systems as well. The broadness and level of sophistication of this
technique is documented in many monographs and reviews, see for example
\cite{Allan,Frenkel,mdhere}. Here we discuss the extension of MD to quantum
systems (QMD). There have been many attempts in this direction which differ
from one another, depending on the type of system under consideration. One
direction of QMD has been developed for condensed matter systems and will not
discussed here, e.g. \cite{fermid}. In this chapter we are dealing with unbound
electrons as they occur in gases, fluids or plasmas. Here, one strategy is to
replace classical point particles by wave packets, e.g.
\cite{fermid,KTR94,zwicknagel06} which is quite successful. At the same time,
this method struggles with problems related to the dispersion of such a packet
and difficulties to properly describe strong electron-ion interaction and bound
state formation. We, therefore, avoid such restrictions and consider a
completely general alternative approach. We start discussion of quantum
dynamics from a general consideration of quantum distribution functions.Comment: 18 pages, based on lecture at Hareaus school on computational phyics,
Greifswald, September 200
Interacting electrons in a one-dimensional random array of scatterers - A Quantum Dynamics and Monte-Carlo study
The quantum dynamics of an ensemble of interacting electrons in an array of
random scatterers is treated using a new numerical approach for the calculation
of average values of quantum operators and time correlation functions in the
Wigner representation. The Fourier transform of the product of matrix elements
of the dynamic propagators obeys an integral Wigner-Liouville-type equation.
Initial conditions for this equation are given by the Fourier transform of the
Wiener path integral representation of the matrix elements of the propagators
at the chosen initial times. This approach combines both molecular dynamics and
Monte Carlo methods and computes numerical traces and spectra of the relevant
dynamical quantities such as momentum-momentum correlation functions and
spatial dispersions. Considering as an application a system with fixed
scatterers, the results clearly demonstrate that the many-particle interaction
between the electrons leads to an enhancement of the conductivity and spatial
dispersion compared to the noninteracting case.Comment: 10 pages and 8 figures, to appear in PRB April 1
Temperature-dependent quantum pair potentials and their application to dense partially ionized hydrogen plasmas
Extending our previous work \cite{filinov-etal.jpa03ik} we present a detailed
discussion of accuracy and practical applications of finite-temperature
pseudopotentials for two-component Coulomb systems. Different pseudopotentials
are discussed: i) the diagonal Kelbg potential, ii) the off-diagonal Kelbg
potential iii) the {\em improved} diagonal Kelbg potential, iv) an effective
potential obtained with the Feynman-Kleinert variational principle v) the
``exact'' quantum pair potential derived from the two-particle density matrix.
For the {\em improved} diagonal Kelbg potential a simple temperature dependent
fit is derived which accurately reproduces the ``exact'' pair potential in the
whole temperature range. The derived pseudopotentials are then used in path
integral Monte Carlo (PIMC) and molecular dynamics (MD) simulations to obtain
thermodynamical properties of strongly coupled hydrogen. It is demonstrated
that classical MD simulations with spin-dependent interaction potentials for
the electrons allow for an accurate description of the internal energy of
hydrogen in the difficult regime of partial ionization down to the temperatures
of about K. Finally, we point out an interesting relation between the
quantum potentials and effective potentials used in density functional theory.Comment: 18 pages, 11 figure
Dynamical Properties and Plasmon Dispersion of a Weakly Degenerate Correlated One-Component Plasma
Classical Molecular Dynamics (MD) simulations for a one-component plasma
(OCP) are presented. Quantum effects are included in the form of the Kelbg
potential. Results for the dynamical structure factor are compared with the
Vlasov and RPA (random phase approximation) theories. The influence of the
coupling parameter , degeneracy parameter and the form
of the pair interaction on the optical plasmon dispersion is investigated. An
improved analytical approximation for the dispersion of Langmuir waves is
presented.Comment: 23 pages, includes 7 ps/eps-figures and 2 table