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

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 B_Ta=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 ΔP_th=[αB_T(V_a)+(∂B_T/∂T)_V ln(V_a/V)]ΔT. When αB_T(V_a) is assumed to be constant, the fit to the data yielded αB_T(V_a)=0.0033 GPa/K 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 (∂B_T/∂T)_V=0.000 87. [ABSTRACT FROM AUTHOR]