UCL Discovery

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 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 Delta P-th=[alpha B-T(V-a)+(partial derivative B-T/partial derivative T)(V) ln(V-a/V)]Delta T. When alpha B-T(V-a) is assumed to be constant, the fit to the data yielded alpha B-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 (partial derivative B-T/partial derivative T)(V)=0.000 87. (c) 2008 American Institute of Physics.