Quantum molecular dynamics simulations of transport properties in liquid and dense-plasma plutonium

Abstract

We have calculated the viscosity and self-diffusion coefficients of plutonium in the liquid phase using quantum molecular dynamics (QMD) and in the dense-plasma phase using orbital-free molecular dynamics (OFMD), as well as in the intermediate warm dense matter regime with both methods. Our liquid metal results for viscosity are about 40% lower than measured experimentally, whereas a previous calculation using an empirical interatomic potential (modified embedded atom [LANL publication number: LA-UR-10-07728]

Behavior of the coupling parameter under isochoric heating in a high-Zplasma

“…4 that this rough estimation is quite good compared to the OFMD results, even if the characteristic frequencies of the OCP do not match those of the screened OFMD system [4,25]. The scaling with temperature (T b ) gives b = 0.625 between 100 and 1000 eV and remains consistent with the results for U (b=0.557) [22] and Pu (b=0.548) [9].…”

“…We have found similar behavior of the coupling constant for other high Z materials, namely Pu and U (references [9] and [22]). The occurrence of the plateau is directly linked to the atomic number and density and will be the subject of a detailed subsequent paper.…”

“…Unfortunately, since no precise definition of the ionization state exists, we will use * jean.clerouin@cea.fr the usual Thomas-Fermi (TF) and Thomas-Fermi-Dirac (TFD) estimations at finite temperature. To determine the structural and transport properties, we will also use Orbital Free Molecular Dynamics simulations (OFMD), whose quality has been proven in this dense hot regime [3][4][5][6][7][8][9]. In this study, we focus on tungsten, which with a charge number Z=74, offers a wide range of thermodynamic states before reaching total ionization.…”

Transport properties of an asymmetric mixture in the dense plasma regime

“…This involves a variety of methods, all of which solve the electronic structure, examples include quantum molecular dynamics [24], path integral Monte Carlo (PIMC) [25,26], and orbital free molecular dynamics (OFMD) [27]. Here we will focus on the use of OFMD, which has proven accurate for extracting equations-of-state and mass transport properties for the WDM regime and up to the dense plasma regime [28][29][30][31][32].…”

Thermophysical properties of hydrogen-helium mixtures: Re-examination of the mixing rules via quantum molecular dynamics simulations

“…Different from the self-diffusion coefficient, which involves single-particle correlations and attains significant statistical improvement from averaging over the particles, the viscosity depends on the entire system and thus needs very long trajectories so as to gain statistical accuracy. To shorten the length of the trajectory, we use empirical fits [35] to the integrals of the autocorrelation functions. Thus, extrapolation of the fits to t → ∞ can more effectively determine the basic dynamical properties.…”