Pair potentials for warm dense matter and their application to x-ray Thomson scattering in aluminum and beryllium

TL;DR

This paper introduces an efficient first-principles NPA-HNC model for warm dense matter, accurately predicting X-ray Thomson scattering spectra in aluminum and beryllium without common simplifying assumptions, validated against experiments and DFT-MD.

Contribution

The paper presents a novel NPA-HNC approach that provides accurate pair-potentials and pseudopotentials for warm dense matter, improving interpretation of XRTS data over traditional models.

Findings

NPA-HNC results closely match DFT-MD simulations.

Yukawa screening models produce misleading results.

The model accurately predicts structure factors, compressibilities, phonons, and conductivities.

Abstract

Ultrafast laser experiments yield increasingly reliable data on warm dense matter, but their interpretation requires theoretical models. We employ an efficient density functional neutral-pseudoatom hypernetted-chain (NPA-HNC) model with accuracy comparable to ab initio simulations and which provides first-principles pseudopotentials and pair-potentials for warm-dense matter. It avoids the use of (i) ad hoc core-repulsion models and (ii) "Yukawa screening", and (iii) need not assume ionelectron thermal equilibrium. Computations of the x-Ray Thomson scattering (XRTS) spectra of aluminum and beryllium are compared with recent experiments and with density-functional-theory molecular-dynamics (DFT-MD) simulations. The NPA-HNC structure factors, compressibilities, phonons and conductivities agree closely with DFT-MD results, while Yukawa screening gives misleading results. The analysis of the XRTS data for two of the experiments, using two-temperature quasi-equilibrium models, is supported by calculations of their temperature relaxation times.