Nonempirical Semi-local Free-Energy Density Functional for Matter Under Extreme Conditions

TL;DR

This paper introduces a new semi-local exchange-correlation free-energy functional for density functional theory, accurately modeling matter under extreme conditions across various temperatures and densities.

Contribution

It presents the first systematic construction of a generalized gradient approximation XC free-energy functional based on rigorous constraints, improving predictions for warm dense matter.

Findings

Accurately predicts deuterium equation of state matching path integral Monte Carlo results.

Effectively models pressure shifts in hot electrons and low-density aluminum.

Provides correct temperature dependence and known limits in various regimes.

Abstract

Realizing the potential for predictive density functional calculations of matter under extreme conditions depends crucially upon having an exchange-correlation (XC) free energy functional accurate over a wide range of state conditions. Unlike the ground-state case, no such functional exists. We remedy that with systematic construction of a generalized gradient approximation XC free-energy functional based on rigorous constraints, including the free energy gradient expansion. The new functional provides the correct temperature dependence in the slowly varying regime and the correct zero-T, high-T, and homogeneous electron gas limits. Its accuracy in the warm dense matter regime is attested by excellent agreement of the calculated deuterium equation of state with reference path integral Monte Carlo results at intermediate and elevated T. Pressure shifts for hot electrons in compressed static fcc Al and for low density Al demonstrate the combined magnitude of thermal and gradient effects handled well by this functional over a wide T range.