Hydrostatic Equation of State of bcc Bi by Directly Solving the Partition Function

Abstract

Body-centered cubic bismuth (Bi) is considered to be an enticing pressure marker, and, therefore, it is highly desirable to command its accurate equation of state (EOS). However, significant discrepancies are noted among the previous experimental EOSs. In the present work, an EOS of up to 300 GPa is theoretically obtained by solving the partition function via a direct integral approach (DIA). The calculated results nearly reproduce the hydrostatic experimental measurements below 75 GPa, and the deviations from the measurements gradually become larger with increasing pressure. Based on the ensemble theory of equilibrium state, the DIA works with high precision particularly in high-pressure conditions, so the hydrostatic EOS presented in this work is expected to be a reliable pressure standard.