Density functional theory plane-wave/pseudopotential calculations of the equation of state of rhenium in the terapascal regime

Abstract

The equation of state (EOS) of hexagonal close-packed rhenium has been previously determined up to 1.5 TPa (V/V0 = 0.46) using all-electron (AE) density functional theory (DFT) including core relativistic effects [Phys. Rev. B 100, 174107 (2019)]. This work focuses on assessing the validity of pseudopotentials at such high-pressures, above 1 terapascal (TPa), by comparing the EOS obtained using plane-wave/pseudopotentials (PW/PPs) with previous AE calculations. Both ONCV pseudopotentials tested (PBE and PBEsol) yield results in good agreement with all-electron calculations. The fitted parameters of the Rose-Vinet EOS, the bulk modulus, B0 (380(2) GPa and 379(3) GPa for the PBE and PBEsol PPs), and its pressure derivative, B0'(4.58(2) and 4.59(3) for the PBE and PBEsol PPs), are in good agreement with previous all-electron results (B0=367(5) GPa and B0'=4.64(3)). The agreement is worse for the equilibrium volume at zero pressure, V0 (199.9(2) Bohr3 and 199.2(2) Bohr3 for PBE and PBEsol PPs, versus 196.7(3) Bohr3 for AE). Even so, for a given V/V0 ratio, the pressures estimated using the EOS derived from the PPs and AE calculations are in very good agreement, thus suggesting that the PPs used in this study are valid even at such high compression regime.