Structure and thermodynamic properties of liquid cesium at pressures below 10 GPa and temperatures below 4000 K according to the molecular dynamics data

Abstract

The models of cesium at temperatures of up to 4000 K, compressions of up to Y = V/V0 = 0.3, and pressures of up to 24 GPa were constructed by the molecular dynamics (MD) method using the ЕАМ interparticle potential. The thermodynamic properties of the models are presented in the tables. The compressibility factors were calculated: Z = pV/RT. The thermodynamic properties of the MD models were in satisfactory agreement with experiment in the range of parameters under study at a cesium density of higher than 1.2 g/cm3. The behavior of the models in the region of the van der Waals loop was analyzed. The calculated critical temperature of cesium Tc was shown to be ~1950 ± 25 K, approximating the real temperature, the density was ~0.53 g/cm3, the pressure ~0.015 GPa, and the compressibility factor Z = pV/RT ≈ 0.23. The states with a unity factor Z = 1 were observed at pressures below 0.20 GPa (at 2800 K); the temperature dependence of the density of the models with Z = 1 was almost linear, and the Boyle temperature TB was 7160 K; the ratio Tc/TB = 0.269 was very close to that for mercury (0.276). In the pressure and temperature ranges under study, the inversion of the Joule–Thomson coefficient was not observed, but took place at densities below 1.2 g/cm3. The structure of the liquid changed when the degree of compression of the cesium models changed from 0.54 to 0.52. This was reflected by a change in the degree of asymmetry of the first peak of the radial distribution function. An analysis of the structural data of the models of liquid sodium, potassium, and rubidium showed that the structure of these metals also experienced similar changes near the degree of compression 0.5; these changes in alkali metals are not related to the 6s → 5d electron transition.