Ion-ion dynamic structure factor, acoustic modes, and equation of state of two-temperature warm dense aluminum

Abstract

The ion-ion dynamical structure factor and the equation of state of warm dense aluminum in a two-temperature quasiequilibrium state, with the electron temperature higher than the ion temperature, are investigated using molecular-dynamics simulations based on ion-ion pair potentials constructed from a neutral pseudoatom model. Such pair potentials based on density functional theory are parameter-free and depend directly on the electron temperature and indirectly on the ion temperature, enabling efficient computation of two-temperature properties. Comparison with ab initio simulations and with other average-atom calculations for equilibrium aluminum shows good agreement, justifying a study of quasiequilibrium situations. Analyzing the van Hove function, we find that ion-ion correlations vanish in a time significantly smaller than the electron-ion relaxation time so that dynamical properties have a physical meaning for the quasiequilibrium state. A significant increase in the speed of sound is predicted from the modification of the dispersion relation of the ion acoustic mode as the electron temperature is increased. The two-temperature equation of state including the free energy, internal energy, and pressure is also presented.

Kinetic energy functionals and the $N$-representability of the electron pair-density given by the classical map hyper-netted-chain (CHNC) method

“…This has of course been verified in many other calculations during past decades, even with respect to complex fluids like warm dense carbon, silicon etc., where there are covalent bonding effects as well [22,23]. A similar verification is available in the context of ion-dynamical calculations [69,70].…”

Simple pair-potentials and pseudo-potentials for warm-dense matter and general applications

“…It is of interest to see how the pair-potential used in the NPA brings in the three-body energy and such 'multicenter' terms via the ion-ion XC functional used in the NPA approach. Of course, if classical MD is used with the NPA pair-potentials [22,49,53], then the ion-ion correlations are automatically built up by the long-range pair-interactions. Such simulations yield the g ii (r), but the calculation of the total energy requires contributions from the electron subsystem in calculating the total energy, as discussed in Ref.…”

“…Then a quasi-thermodynamic situation exists for time scales τ such that τ ee ≪ τ ≪ τ ii ≪ τ ei , where τ ss ′ is the temperature relaxation time [21] between species s and s ′ . The NPA approach can be generalized to two-temperature WDMs and explicit NPA calculations are available [21,22].…”

Temperature separation under compression of moderately coupled plasma

“…2015), warm dense matter (Harbour et al. 2018), turbulent fluids and plasmas (Volkov 1999; Davidovits & Fisch 2019) and the intergalactic medium (Ricotti, Gnedin & Shull 2000). Other examples of quasi-EOS include the compression of plasmas laden with either linear waves (Schmit, Dodin & Fisch 2010) or nonlinear waves (Schmit et al.…”