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M. Bonitz

Publications and source records attributed to M. Bonitz.

At least 145 records · Page 8Linked to original sources
arXiv2001

Internal energy of high density Hydrogen: Analytical approximations compared with path integral Monte Carlo calculations

The internal energy of high-density hydrogen plasmas in the temperature range $T = 10,000 ... 50,000 K$ is calculated by two different analytical approximation schemes (method of effective ion-ion interaction potential - EIIP and Padé approach within the chemical picture - PACH) and compared with path integral Monte Carlo results. Reasonable agreement between the results obtained from the three independent calculations is found, the reasons for still existing differences is investigated. Interesting high density phenomena such as the formation of clusters and the onset of crystallization are discussed.

physics.plasm-ph↗
arXiv2001

Phase Transition in Strongly Degenerate Hydrogen Plasma

Direct fermionic path-integral Monte-Carlo simulations of strongly coupled hydrogen are presented. Our results show evidence for the hypothetical plasma phase transition. Its most remarkable manifestation is the appearance of metallic droplets which are predicted to be crucial for the electrical conductivity allowing to explain the rapid increase observed in recent shock compression measurments.

cond-mat.soft↗
arXiv2001

Plasmon dispersion of a weakly degenerate nonideal one-component plasma

Classical Molecular Dynamics simulations (MD) for a one-component weakly degenerate plasma are presented. Using an effective quantum pair potential (Kelbg potential), the dynamic structure factor and the dispersion of Langmuir waves are computed. The influence of the coupling strength $Γ$ and degree of degeneracy $ρΛ^3$ on these properties is discussed. The results are compared with predictions of mean-field theories.

cond-mat.str-el↗
arXiv2001

Dielectric properties of correlated quantum plasmas

Results for the dynamic structure factor of a one-component plasma are presented for the situations of strong coupling and weak degeneracy and strong degeneracy and weak coupling. Possibilities to obtain rigorous results when both, coupling and degeneracy are large are discussed.

cond-mat.stat-mech↗
arXiv2001

Path integral Monte Carlo simulations and analytical approximations for high-temperature plasmas

The results of analytical approximations and extensive calculations based on a path integral Monte Carlo (PIMC) scheme are presented. A new (direct) PIMC method allows for a correct determination of thermodynamic properties such as energy and equation of state of dense degenerate Coulomb systems. In this paper, we present results for dense partially ionized hydrogen at intermediate and high temperature. We give a quantitative comparison with the available results of alternative (restricted) PIMC simulations and with analytical expressions based on iterpolation formulas meeting the exact limits at low and high densities. Good agreement between the two simulations is found up to densities of the order of $10^{24}cm^{-3}$. The agreement with the analytical results is satisfactory up to densities in the range $10^{22}... 10^{23}cm^{-3}$.

astro-ph↗
arXiv2001

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 $10^{-1}$ and $10^2$ 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 $Γ\lesssim 3$ and degeneracy parameter $n_e Λ^3 \lesssim 10$. 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.

physics.plasm-ph↗
arXiv2001

Two-dimensional electron crystals in single and double layers

We present results of Monte-Carlo simulations for finite 2D single and bilayer systems. Strong Coulomb correlations lead to arrangement of particles in configurations resembling a crystal lattice. For binary layers, there exists a particularly rich variety of lattice symmetries which depend on the interlayer separation $d$. We demonstrate that in these mesoscopic lattices there exist two fundamental types of ordering: radial and orientational. The dependence of the melting temperature on $d$ is analyzed, and a stabilization of the crystal compared to a single layer is found.

cond-mat.mes-hall↗
arXiv2001

Kadanoff-Baym equations and non-Markovian Boltzmann equation in generalized T-matrix approximation

A recently developed method for incorporating initial binary correlations into the Kadanoff-Baym equations (KBE) is used to derive a generalized T-matrix approximation for the self-energies. It is shown that the T-matrix obtains additional contributions arising from initial correlations. Using these results and taking the time-diagonal limit of the KBE, a generalized quantum kinetic equation in binary collision approximation is derived. This equation is a far-reaching generalization of Boltzmann-type kinetic equations: it selfconsistently includes memory effects (retardation, off-shell T-matrices) as well as many-particle effects (damping, in-medium T-Matrices) and spin-statistics effects (Pauli-blocking).

cond-mat.stat-mech↗
arXiv2000

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 $Γ$, degeneracy parameter $ρΛ^3$ 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.

physics.plasm-ph↗
arXiv2000

Wigner Crystallization in mesoscopic 2D electron systems

Wigner crystallization of electrons in a 2D quantum dots is reported. It proceeds in two stages: I) via radial ordering of electrons on shells and II) freezing of the inter-shell rotation. The phase boundary of the crystal is computed in the whole temperature--density plane, and the influence of quantum effects and of the particle number is analyzed.

cond-mat.mes-hall↗
arXiv2000

Harmonics generation in electron-ion collisions in a short laser pulse

Anomalously high generation efficiency of coherent higher field-harmonics in collisions between {\em oppositely charged particles} in the field of femtosecond lasers is predicted. This is based on rigorous numerical solutions of a quantum kinetic equation for dense laser plasmas which overcomes limitations of previous investigations.

cond-mat↗
arXiv1999

Quantum kinetic theory for dense Coulomb systems in strong electromagnetic fields

A quantum kinetic theory for correlated charged-particle systems in strong time-dependent electromagnetic fields is developed. Our approach is based on a systematic gauge-invariant nonequilibrium Green's functions formulation. We concentrate on the selfconsistent treatment of dynamical screening and electromagnetic fields which is applicable to arbitrary nonequilibrium situations. Numerical results for the nonlinear plasma heating by the laser field and the electron-ion collision frequency including multi-photon absorption (inverse bremsstrahlung) are presented.

cond-mat.str-el↗
arXiv1999

Thermodynamic Properties of Strongly Degenerate Interacting Fermi Systems

A numerical approach is presented which allows to calculate the equilibrium properties of Fermi systems which are both, strongly coupled and strongly degenerate. Based on a novel path integral representation of the many-particle density operator, quantum and spin effects are included. As an illustration, results for the pressure and energy of an electron-proton plasma are presented.

cond-mat.str-el↗
arXiv1999

Quantum Kinetic Theory for Laser Plasmas. Dynamical Screening in Strong Fields

A quantum kinetic theory for correlated charged-particle systems in strong time-dependent electromagnetic fields is developed. Our approach is based on a systematic gauge-invariant nonequilibrium Green's functions formulation. Extending our previous analysis (Kremp et al., Phys. Rev. E vol. 60, p. 4725 (1999) we concentrate on the selfconsistent treatment of dynamical screening and electromagnetic fields which is applicable to arbitrary nonequilibrium situations. The resulting kinetic equation generalizes previous results to quantum plasmas with full dynamical screening and includes many-body effects. It is, in particular, applicable to the interaction of dense plasmas with strong electromagnetic fields, including laser fields and x-rays. Furthermore, results for the modification of the plasma screening and the longitudinal field fluctuations due to the electromagnetic field are presented.

cond-mat.stat-mech↗
arXiv1999

Real-time Kadanoff-Baym approach to plasma oscillations in a correlated electron gas

A nonequilibrium Green's functions approach to the collective response of correlated Coulomb systems at finite temperature is presented. It is shown that solving Kadanoff-Baym type equations of motion for the two-time correlation functions with the external perturbing field included allows to compute the plasmon spectrum with collision effects in a systematic and consistent way. The scheme has ``built-in'' sum rule preservation and is simpler to implement numerically than the equivalent equilibrium approach based on the Bethe-Salpeter equation.

cond-mat.str-el↗
arXiv1999

Thermodynamic Properties of Correlated Strongly Degenerate Plasmas

An efficient numerical approach to equilibrium properties of strongly coupled systems which include a subsystem of fermionic quantum particles and a subsystem of classical particles is presented. It uses an improved path integral representation of the many-particle density operator and allows to describe situations of strong coupling and strong degeneracy, where analytical theories fail. A novel numerical method is developed, which allows to treat degenerate systems with full account of the spin scatistics. Numerical results for thermodynamic properties such as internal energy, pressure and pair correlation functions are presented over a wide range of degeneracy parameter.

cond-mat.str-el↗
arXiv1999

Kadanoff-Baym Equations with Initial Correlations

The Kadanoff-Baym equations (KBE) are usually derived under the assumption of the weakening of initial correlations (Bogolyubov's condition) and, therefore, fail to correctly describe the short time behavior. We demonstrate that this assumption is not necessary. Using functional derivatives techniques, we present a straightforward generalization of the KBE which allows to include arbitrary initial correlations and which is more general than previous derivations. As a result, an additional collision integral is obtained which is being damped out after a few collisions. Our results are complemented with numerical investigations showing the effect of initial correlations.

cond-mat.stat-mech↗