Characterization of Liquid-Vapor Coexistence in Platinum

Platinum is a standard material for high pressure experiments, yet the liquid-vapor critical behavior is poorly constrained. We present the liquid-vapor critical point and phase boundary using density functional theory based molecular dynamics (DFTMD). The critical behavior is characterized using independent methods: a fit of the DFTMD data to a generalized virial equation of state model and subsequent Maxwell construction on isotherms below the critical temperature, as well as an analysis of the particle trajectories to perform an instantaneous interface calculation from which we estimate the densities of coexisting liquid and vapor. We find these independent estimates of the critical point and liquid-vapor phase boundary give good agreement, significantly improving the phase diagram in this region. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.