Reconstruction of release isentropes based on first-principle simulations

Abstract

In this work we compare different methods of reconstruction of isentropic expansion curves based on quantum molecular dynamics simulation data. The VASP code is used. We analyze accuracy and computational complexity of three methods: the Zel’dovich approach, a method of re-shock Hugoniots and a direct calculation of entropy using the 2PT model. In the first method, an ordinary differential equation for temperature is solved numerically. The second method is based on the feature of the second-order contact of a Hugoniot and isentrope at the same initial point. The density of vibrational states which is reconstructed from a velocity autocorrelation function is used to calculate entropy by the third method. For aluminum the three methods turned out to give very close results for a release isentrope in agreement with experimental data. For molybdenum an experimental release isentrope is well reproduced by the second method.