Molecular dynamics simulation of the structure and thermodynamic properties of liquid rubidium at pressures of up to 10 GPa and temperatures of up to 3500 K

Abstract

The models of rubidium at temperatures of up to 3500 K, degrees of compression of up to Y = V/V₀ = 0.3, and pressures of up to 32 GPa were constructed by molecular dynamics (MD) using the interparticle potential ЕАМ. The thermodynamic properties of the MD models agree satisfactorily with experiment in the range of parameters under study at rubidium densities higher than 0.86 g/cm³. The behavior of the models in the range of the van der Waals loop was analyzed; the calculated critical temperature of rubidium T_c is ∼2250 ± 25 K, density ∼0.41 g/cm³, pressure ∼0.019 GPa, and compressibility factor Z = pV/RT ≈ 0.137. The states with the unity factor Z = 1 were observed at pressures of up to 0.30 GPa (at ∼3000 K); the temperature dependence of the density of the models with Z = 1 is nearly linear, and the Boyle temperature is T_B ≈ 10160 K. The ratio T_c/T_B = 0.221 is close to this value for cesium (0.23) and mercury (0.276). In the temperature and pressure ranges under study, the inversion of the Joule–Thomson coefficient did not take place, but should be observed at pressures of ⩽0.3 GPa and elevated temperatures. It was found that the diffusion coefficient D(T) dependences do not straighten in the usually used coordinates within wide temperature ranges. It was concluded that the structure of the liquid smoothly changes when the rubidium models are compressed and this reveals in the change of the degree of asymmetry of the first peak of the radial distribution function.