High-Pressure Isothermal Equation of State for Materials with Pressure Derivative of the Isothermal Bulk Modulus Less Than Four

A phenomenological isothermal equation of state (EOS) is presented which is more accurate than the Birch-Murnaghan EOS and the Vinet EOS in case of a material (LiH) for which the pressure derivative of the isothermal bulk modulus, K-0' < 4. The present EOS yields results in close agreement with the Hama-Suito universal EOS based on first-principle calculations. The inverted form of the EOS has been found to be useful for calculating the change in volume as a function of pressure. The densities for the entire depth of the lower mantle have been calculated with the help of the present EOS. The results for densities have been found to be in good agreement with seismological data for the lower mantle.