Equation of state and melting transition of argon up to 8000 K and 4 megabars: A molecular dynamics study

Abstract

A new method of determination of temperature-pressure (T-P) dependence of melting with molecular dynamics (MD) simulation is proposed. The main criterion for such a determination is the Gauss principle of least action. The equation P_m = 89.79T _r ^1.646 + 0.9869 where P_m—melting pressure and T_r = T/1000, T in K and P in kbar fits molecular dynamics (MD) results well. An analytical expression which fits MD simulated PVT data can be used as analytical equation of state of argon up to 4000 K and 4000 kbar. The theoretical limit for change of entropy at solid-liquid transition which equals 0.9 R (R-gas constant) is evaluated as correct. However, the same limit for volume change (ΔV/V_s, V_s ,—volume of solid at melting) estimated as 0.025 is incorrect. The Lindemann law which is equivalent to the similarity of radial distribution function of system under melting is found to be valid.