Temperature–pressure–volume equation of state of the B1 phase of sodium chloride

Abstract

The temperature–pressure–volume ( T– P– V) equation of state (EOS) of the B1 phase of NaCl is simulated using the molecular dynamics (MD) method with a breathing shell model (BSM) for Cl ions. Quantum correction to the MD pressures is made using the Wigner–Kirkwood expansion of free energy. Required energy parameters, including Cl breathing parameters, are derived empirically to reproduce the observed molar volume, volume thermal expansion, elastic constants, T– P– V data from piston-cylinder experiments and the temperature dependence of bulk modulus, all as accurately as possible. The observed volume-compression data of the high pressure B2 phase of NaCl are also included to optimize the energy parameters. The MD simulation with BSM is found to accurately reproduce the available measured T– P– V data of both the B1 and the B2 phases. The MD simulated T– P– V EOS is presented up to 30 GPa and 1200 K. Compared with the present MD EOS, the Decker EOS, which has often been used as a practical pressure scale for many years, underestimates pressure by within 4% over the T and P ranges up to 30 GPa and 1200 K. The error in the Decker EOS increases with increasing pressure, with the differences in pressure reaching 0.8 GPa at 300 K and 20 GPa, and 0.7 GPa at 1200 K and 20 GPa.