Improving the accuracy of density functional theory simulations of warm dense matter by including exchange-correlation thermal effects

CASUS Institute Seminar, Deyan Mihaylov, Laboratory for Laser Energetics (LLE), University of Rochester, USA

Deyan joined LLE in 2019 as an assistant scientist. His research interests are focused on application of finite-temperature DFT and nonequilibrium Green’s function methods to improve the description of matter under extreme conditions.

The warm dense matter (WDM) regime, where the Coulomb coupling and the quantum degeneracy plasma parameters are of order unity, is challenging from a theoretical point of view because classical plasma physics approaches are inaccurate in this thermodynamic regime where quantum many-body effects are still important and, on the other hand, standard condensed matter physics methods become intractable. In recent years, ab initio molecular dynamics (AIMD), where classical ions are propagated according to forces obtained by density functional theory (DFT), has proven to be a successful method in accurately describing the WDM regime.

Extending DFT to finite-T has been made possible by the Mermin-Kohn-Sham (MKS) formalism, which provides the means of obtaining a key physical quantity – the T-dependent electron density. To this day, however, much of the MKS DFT-based AIMD simulations of matter in the WDM regime rely on ground-state (T-independent) exchange-correlation (XC) density functionals for evaluating the T-dependent electron density. Recently, there has been progress in the development of finite-T XC functionals: KSDT at the local spin-density approximation (LSDA) and the KDT16 at the generalized-gradient approximation (GGA) level of approximation.

In this talk, Deyan will discuss the development of advanced T-dependent XC functionals based on the KSDT and KDT16 functionals. At the meta-GGA level, his team has developed a finite-T version of SCANL (orbital-free version of the SCAN functional) and at the hybrid level, they have developed a finite-T version of the popular PBE0 functional. Application to calculations of different properties of matter in the WDM regime, such as electronic band gap, equation-of-state and electronic stopping power will also be presented.

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