MODEL DESCRIPTION OF CRYSTALLINE AND LIQUID STATES

New model equations for thermodynamic functions of crystalline and liq uid states are proposed, in which thermal vibrations of atoms near the positions of equilibrium are described in a generalized Debye approxi mation that changes, in the limit of high temperatures and volumes, in to an ideal-gas approximation. The difference of elastic (cold) compon ents of energy and pressure for a liquid and solid, formally associate d with the difference of the heats of vaporization and densities of th ese phases at zero temperatures, is taken into account. A configuratio n component, that is, the quantity characterizing the measure of disor der in the liquid, is introduced in its thermodynamic functions. This component brings about finite values of entropy with formal extrapolat ion of the liquid properties to zero temperatures. For neon, the depen dences of the Debye temperature and cold components of pressure are de termined on the basis of reliable tabulated data for thermodynamic fun ctions. The isotherms of free energy and pressure are constructed at z ero temperature at the triple and critical points, clearly interpretin g the solid-liquid, solid-gas and liquid-gas phase transitions. A geom etric interpretation (the area rule) of the solid-liquid phase transit ion is suggested.