About the gold properties and the approximations used to calculate high-pressure high-temperature properties

Using an analytical method that uses the paired potential of the Mie-Lennard-Jones interatomic interaction, the properties of gold (fcc-Au) are calculated in the range of temperatures: T = 10-1337 K and pressures: P = 0-110 GPa. The following properties were calculated: state equation, Debye temperature, first and second Griineisen parameters, elastic modulus (B-T), thermal expansion coefficient (alpha(p)), isochoric (C-v) and isobaric (C-p) heat capacity, specific surface energy. The obtained results showed good agreement with the experimental and theoretical data of other authors. It was shown that there is a certain temperature T-B in which the thermoelastic parameter alpha(p).B-T does not change during isothermal compression of the crystal. At T > T-B, the alpha(p).B-T function increases, and at T < T-B , the alpha(p).B-T function decreases with an isothermal increase in pressure. For fcc-Au has been received T-B = 132 K. For the first time, the derivatives of these properties were calculated both by temperature along three isobars and by pressure along three isotherms. It was shown that the isotherms of the baric derivative of elastic modulus B'(P) intersect at the point: P = 21.58 GPa, and B'(P) = 7.43. At P < 21.58 GPa, the B'(P) function increases linearly, and at P > 21.58 GPa, the B'(P) function weakly decreases with an isobaric increase in temperature. It was shown that the isotherm of the baric derivative of the isochoric heat capacity C-v'(P) has a minimum, and the isotherm of the baric derivative of the isobaric heat capacity C-p' (P) has both a minimum and a maximum. Based on the obtained dependencies, some approximations, which are used to calculate the properties of the crystal under high P-T conditions, have been analyzed.