Effects of the Electronic Subsystem on the Thermodynamic Properties of Rhodium

The properties of rhodium (Rh) have been calculated analytically, both without and taking into account the electronic subsystem (ELS). The ELS effect on the baric (P) and temperature (T) dependences of Rh properties has been studied. It is shown that when ELS is taken into account, both the isotherms of the equation of state and the P–T dependences of the following properties change negligibly: the Debye temperature, the Gruneisen parameter, the elastic modulus (B), the specific surface energy (σ), the isochoric derivative of the σ function with respect to temperature and the isothermal derivative of the σ function with respect to pressure. The pressure dependences of the derivatives of these properties also do not change. When ELS is taken into account in the region of high temperatures and low pressures, the following properties noticeably change: the thermal expansion coefficient (α), isochoric and isobaric (C) heat capacities, the α·B product, and the isobaric derivative of the σ function with respect to temperature. When ELS is taken into account, the agreement of our calculated dependences α(T,P) and C(T,P) with experimental data improves markedly. With increasing pressure, the contribution of ELS to the Rh properties decreases. It is shown that at a certain temperature (Birch temperature, T), the product α·B = (∂P/∂T) does not change with isothermal pressure increase. At T< T, the α·B function decreases, and at T > T the α·B function increases with an isothermal increase in pressure. For Rh, T = 188.5K was obtained, and the T value does not depend on ELS accounting. Calculations of the baric dependence of the melting point T(P) have shown that when ELS is taken into account, the dependence of T(P) for Rh decreases slightly. However, the contribution of ELS to the T(P) dependence is very small even at low pressures.