First-principles thermal equation of state of fcc iridium

Abstract

The thermal equation of states for fcc iridium (Ir) is obtained from first-principles molecular dynamics up to 3000 K and 540 GPa. The equation of state (EoS) is globally fitted to a simplified free energy model and various parameters are derived. The theoretical principal Hugoniot is compared with shockwave experiments, where discrepancy suggests formation of new Ir phases. A few representative EoS parameters, such as bulk modulus KT , thermal expansivity α, Grüneisen parameter γ, and constant pressure capacity CP , Debye temperature, ΘD are computed to compare with experimental data.