Liquid-vapor coexistence of platinum from ab initio simulations

Platinum is a standard material for high pressure experiments, yet estimates of the liquid-vapor critical temperature and density span nearly 7000 K and 2 g/cm3. Here, we present the results of the first systematic investigation of liquid-vapor coexistence and critical behavior of platinum using density functional theory based molecular dynamics. We compare critical point parameters and liquid-vapor phase boundaries obtained from a fit to an equation of state spanning liquid and vapor states and a subsequent Maxwell construction and, separately, from an instantaneous interface calculation from which we estimated the densities of coexisting liquid and vapor. We find good agreement in the estimated critical point obtained from these calculations but the binodal shows considerably more variation, especially at lower temperatures. Overall, our estimated critical point of ρc = 5.03 g/cm3, Tc = 7690 K, and Pc = 2.17 kbar is significantly cooler than many previous estimates based on more indirect methods.