Electronic thermal pressure and equation of state of gold at high temperature and high pressure

Abstract

We calculate the electronic thermal pressure of Au at temperatures up to 20 000 K for four compressions η=1−V/V0=0.0, 0.12, 0.24, and 0.36 (where V is the volume and V0 the ambient volume), using the uniform electron gas model with the random-phase approximation for the exchange-correlation potential. We show the isochoric electronic thermal pressure increases essentially in proportion to the square of temperature T2, which is in contrast to the result from the usual Mie–Grüneisen–Debye-type treatment where the isochoric thermal pressure increases linearly with T above the Debye temperature. We find the isochoric electronic thermal pressure difference from 300 K is relatively insensitive to compression η, and is insignificant at temperatures less than a few thousand K, having the values of 0.087, 0.549, and 2.065 GPa at T=2000, 5000, and 10 000 K, respectively, at η=0.0. The accuracy of previously proposed T−P−V equations of state of Au is discussed in relation to their use as pressure calibration standards at high temperature and high pressure.