An accurate analytical parametrization for the exchange-correlation free energy of the homogeneous electron gas, including interpolation for partial spin-polarization, is derived via thermodynamic analysis of recent restricted path integral Monte-Carlo (RPIMC) data. This parametrization constitutes the local spin density approximation (LSDA) for the exchange-correlation functional in density functional theory. The new finite-temperature LSDA reproduces the RPIMC data well, satisfies the correct high-density and low-and high-T asymptotic limits, and is well-behaved beyond the range of the RPIMC data, suggestive of broad utility.
PACS numbers:The homogeneous electron gas (HEG) is a fundamentally important system for understanding many-fermion physics. In the absence of exact analytical solutions for its energetics, high-precision numerical results have been critical to insight. Recently published [1] restricted path integral Monte Carlo (RPIMC) data for the HEG over a wide range of temperatures and densities open the opportunity to obtain closed form expressions for HEG thermodynamics, in particular the exchange and correlation (XC) contributions. Such expressions extracted from Monte Carlo data are well-known for the zero-T HEG, where they have played a major role in understanding inhomogeneous electron-system behavior. We provide the corresponding thermodynamical expressions for wide temperature and density ranges.Density functional theory (DFT) is the motivating context. For ground-state DFT, the most basic exchangecorrelation (XC) density functional is the local density approximation (LDA). It approximates the local XC energy per particle, ε xc , as the value for the HEG at the local density, ε LDA xc (n(r)) ≈ ε HEG xc (n)| n=n(r) [also see Eq. (3) [5] for the spin-polarized T = 0 K HEG also validate the spininterpolation formulae used in that case, the local spin density approximation (LSDA). All more refined ε xc approximations reduce to the LSDA in the weak inhomogeneity limit.Finite-temperature DFT [6-8] increasingly is being used to study matter under diverse density and temperature conditions [9][10][11][12][13][14]. In it, the XC free-energy is defined by decomposition of the universal free-energy density functional (independent of the external potential). With the T -dependence suppressed for now, that functional isThe first two terms are the non-interacting kinetic energy and entropy (also known as the Kohn-Sham KE and entropy), F H [n] is the classical electron-electron Coulomb energy, and the XC free energy by definition iswith T [n] and S[n] the interacting system kinetic energy and entropy and U ee [n] the full quantum mechanical electron-electron interaction energy. Just as for T = 0 K, the existence theorems of finite-T DFT are not constructive for F xc , so approximations must be devised. Common practice [9] in simulations is to use a. This gives only the implicit T -dependence provided by n(r, T ). However, there is substantial evidence from both finite-T Hartree-Fock [12,15] and finite-T exac...