Equation of state for tantalum from relativistic linear combinations of Gaussian-type orbitals calculations

Abstract

The zero-temperature equation of state (EOS) for tantalum (Ta) is calculated to 2.5 Mbar with the relativistic linear combinations of Gaussian type orbital--fitting-function (LCGTO-FF) method, for two density functional models: the local density approximation (LDA) and the generalized gradient approximation (GGA). The EOS is determined both with and without spin-orbit coupling included. The effect of spin-orbit coupling is found to be nearly negligible over the compression range considered, in sharp disagreement with a previous calculation using the full-potential linear muffin-tin orbital method. A serious discrepancy between 300 K diamond anvil cell data and reduced shock data for Ta is shown to result from an underestimate of the Grueneisen parameter during the reduction of the shock data. The GGA model reproduces the zero-pressure properties of Ta quite well, while the high-pressure EOS data is in better accord with the LDA calculations. Neither model provides an adequate representation for the EOS over the full range of the data.