Ab initio molecular dynamics simulations for thermal equation of state of B2 -type NaCl

Abstract

The pressure as a function of volume and temperature has been investigated for B2 -type NaCl over the pressure range of 20-360 GPa and at temperatures between 300 and 3000 K. The simulations were performed using ab initio molecular dynamics method within the density-functional theory framework. A Vinet equation of state fitted to the 300 K data yielded a bulk modulus of BTa =128.66 GPa and a pressure derivative of B Ta ′ =4.374 at standard state pressure of 30 GPa. The thermal pressure contribution was determined to be of the form Δ Pth = [α BT (Va) + ( BT T)V ln (Va V)] ΔT. When α BT (Va) is assumed to be constant, the fit to the data yielded α BT (Va) =0.0033 GPaK at standard volume, corresponding to the pressure of 30 GPa. In contrast, the volume dependence of the thermal pressure was very small, and fitting yielded ( BT T)V =0.000 87. © 2008 American Institute of Physics.