THE DEPENDENCE OF THE ANDERSON-GRUNEISEN PARAMETER DELTA-T UPON COMPRESSION AT EXTREME CONDITIONS

The parameter delta(T) is a dimensionless thermoelastic parameter important in thermodynamic studies involving high temperature at high pressure. We give a brief history of attempts to define delta(T) in terms of fundamental interatomic potentials. We show that ab initio calculations provide a way to find delta(T)(eta, T)(where eta = V/V0), since it is possible to find the minimum in the isochoric B(T) vs T data arising from the ab initio analysis (B(T) is the isothermal bulk modulus). The method is demonstrated for MgO, where delta(T) is calculated over a wide eta, T field. We find delta(T) decreases at high compression, but is independent of T. Knowledge of delta(T)(eta, T) is important to find the high P-high T behavior of a number of important properties in thermal physics, including entropy, thermal expansivity, thermal pressure and the Gruneisen parameter.