First-principles electronic thermal pressure of metal Au and Pt

Electronic thermal pressures (ETP's) of metal Au and Pt are predicted by first-principles electronic structure calculations based on the density functional theory in order to refine their thermal equations of state (EOS) which are frequently used as pressure scales in in situ high-pressure and high-temperature experiment. We find a large difference in the magnitude of ETP's for Au and Pt, which can be attributed to the different positions of the Fermi level. The ETP for Au is considerably smaller than it for Pt. The latter reaches 0.85 GPa at 2000 K, whereas the former is only 0.05 GPa at the same temperature. We also find a different temperature dependence of the ETP's of Au and Pt under high temperature, which arises from the different manner of thermal excitation. It is illustrated that the corrections of the ETP for known EOS of Au and Pt becomes substantially important with increasing temperature, and the ETP can perfectly compensate for the measured discrepancy of pressure values determined by previous EOS of Au and Pt.