Equation of state for metals based on Thomas–Fermi model

To analyze the physical processes at high energy densities, an adequate describing the ther-modynamic properties of matter over a broad region of states including both the condensed phase under normal conditions and plasma at high pressures and temperatures is required [1]. In the present paper a semiempirical equation-of-state model, which is based on Thomas– Fermi theory [2], is proposed. According to this model, the Helmholtz free energy for matter is considered as a sum of three components, F(V;T) = Fc(V)+Fa(V;T)+Fe(V;T); (1) describing the elastic part of interaction at T = 0 K (Fc) and the thermal contributions of atoms (Fa) and electrons (Fe). The first and second components in Eq. (1) are given by interpolation formulae, the third is calculated within the framework of the Thomas–Fermi model [2]. The volume dependence of the elastic energy under compression σc> 1 (where σc =V0c=V, V0c is the specific volume at P = 0 and T = 0 K) is given by the relation [3] Fc(V) = a0V0c lnσc3V0c 3 i=1 ai