Influence of finite temperature exchange-correlation effects in hydrogen

Abstract

We use density functional molecular dynamics (DFT-MD) to study the effect of finite temperature exchange-correlation (xc) in Hydrogen. Using the Kohn-Sham approach, the xc energy of the system, Exc(rs) is replaced by the xc free energy fxc(rs, Θ) within the local density approximation (LDA) based on parametrized path integral Monte Carlo (PIMC) data for the uniform electron gas (UEG) at warm dense matter (WDM) conditions. We observe insignificant changes in the equation of state (EOS) at the region of metal-insulator transition compared to the regular LDA form, whereas significant changes are observed for T>10000 K, i.e., in the important WDM regime. Thus, our results further corroborate the need for temperature-dependent xc functionals for DFT simulations of WDM systems. Moreover, we present the first finite-temperature DFT results for the EOS of Hydrogen in the electron liquid regime up to rs = 14 and find a drastic impact (the EOS changes by more than 20%) of thermal xc effects, which manifests at lower temperatures compared to WDM. We expect our results to be important for many applications beyond DFT, like quantum hydrodynamics and astrophysical models.

Momentum distribution of the uniform electron gas at finite temperature: Effects of spin polarization

“…Phenomenologically, these conditions manifest as the highly nontrivial interplay of quantum effects, Coulomb coupling, and thermal excitations, which renders WDM theory a most formidable challenge [47,48]. Coming back to the UEG, it has become clear that previous groundstate descriptions of the UEG are not sufficient for applications in the WDM regime [49][50][51]. This has sparked a surge of developments in the field of fermionic QMC simulations at finite temperatures [52][53][54][55][56][57][58][59][60][61][62][63] (see Ref.…”

“…[64] for a review), which has culminated in the first accurate parametrizations of the exchange-correlation free energy of the UEG at WDM conditions [65][66][67][68]. In particular, this allows for thermal density functional theory simulations on the level of the local density approximation [49,50], and constitutes the basis for the development of more sophisticated functionals that explicitly take into account the temperature [69,70]. Further progress on the UEG at WDM conditions includes the characterization of linear-response properties such as the static local field correction [71][72][73][74], numerical and theoretical results for the nonlinear electronic density response [75,76], and even the study of dynamic quantities based on the analytic continuation of imaginary-time correlation functions [9,71,[77][78][79].…”

First-principles derivation and properties of density-functional average-atom models

“…We first apply our AA model to the Hydrogen atom. Besides being an element of high interest in the WDM regime in its own right [140], the Schrödinger equation can be solved exactly for the Hydrogen atom and thus results for approximate XC functionals can be easily benchmarked.…”

Nonlinear electronic density response of the warm dense electron gas: multiple perturbations and mode coupling

“…This interest in the properties of WDM has led to a spark of new developments in the QMC simulation of the UEG at finite temperature [17][18][19][20][21][22][23][24][25], which culminated in the first accurate parametrization of the exchangecorrelation (XC) free energy f xc covering the entire relevant range of densities and temperatures [8,[26][27][28]. These new XC-functionals have already been utilized for thermal DFT simulations of WDM [29,30], which has further substantiated the impact of thermal effects on material properties for some parameters. * t.dornheim@hzdr.de…”