Comparison of density functional approximations and the finite-temperature Hartree-Fock approximation in warm dense lithium

摘要

We compare the behavior of the finite-temperature Hartree-Fock model with that of thermal density functionalntheory using both ground-state and temperature-dependent approximate exchange functionals. The test systemnis bcc Li in the temperature-density regime of warm dense matter (WDM). In this exchange-only case, therenare significant qualitative differences in results from the three approaches. Those differences may be importantnfor Born-Oppenheimer molecular dynamics studies of WDM with ground-state approximate density functionalsnand thermal occupancies. Such calculations require reliable regularized potentials over a demanding range ofntemperatures and densities. By comparison of pseudopotential and all-electron results at T = 0 K for small Linclusters of local bcc symmetry and bond lengths equivalent to high density bulk Li, we determine the densitynranges for which standard projector augmented wave (PAW) and norm-conserving pseudopotentials are reliable.nThen, we construct and use all-electron PAWdata sets with a small cutoff radius that are valid for lithium densitiesnup to at least 80 g/cm3.