Non-empirical Semi-local Free-Energy Density Functional for Warm Dense Matter*

Realizing the potential for predictive density functional calculations of warm dense matter
(WDM) depends crucially upon having an exchange-correlation (XC) free-energy functional
that is accurate over a wide range of state conditions. Use of a ground-state functional
completely misses the explicit temperature (T) dependence. The KSDT local density
approximation [1] XC free-energy functional has the proper temperature-dependence for the
homogeneous electron gas, but it misses combined thermal-inhomogeneity XC effects when
applied to inhomogeneous systems. We remedy that with systematic construction of a
generalized gradient approximation XC free-energy functional (KDT16) [2] based on rigorous
constraints, including the free-energy gradient expansion. The new functional provides the
correct T-dependence in the slowly varying regime and the correct zero-T,
high-T, and homogeneous electron gas limits. Its accuracy in the WDM regime is
attested by excellent agreement of the calculated deuterium equation of state with reference
path integral Monte Carlo results at intermediate and elevated temperatures.
Refs: 1. VVK et. al., PRL 112, 076403 (2014); 2. VVK, JWD, SBT, PRL (2017); arXiv:1612.06266.