Molecular-dynamics simulations for the shock Hugoniot meltings of Cu, Pd and Pt

We perform molecular-dynamics simulations to study the shock melting of transition metals such as Cu, Pd and Pt on the basis of an embedded-atom method. Using the coupling-constant integration method, the Gibbs free energies of the crystalline and liquid phases are calculated as a function of pressure and temperature, so that the melting curves are obtained, up to 3-4 Mbar. We find the melting properties near zero pressure to be in good agreement with experiments. For each metal, we compare the melting curve with the Hugoniot equations of state for the solid and liquid phases and determine the melting region of the shock Hugoniot. The Hugoniot melting of Cu is found to begin at 1.9 Mbar and to end at 2.25 Mbar, in good agreement with experimental data. During the shock compression, we find that the pressure region where the Hugoniot melting occurs increases almost linearly with increase of the ionic mass.