First-principles equations of state for simulations of shock waves in silicon

We have calculated a thermodynamically complete equation of state for silicon, based on ab initio predictions of the electron ground states and quasiharmonic phonons, and incorporating phase transitions between crystal structures. The equation of state was in reasonable agreement with data on the shock Hugoniot. We also used the equation of state in continuum mechanical simulations to investigate the splitting of a shock wave, caused by phase transition from the diamond structure. Good agreement is observed, which can be made exact by adjusting the ab initio results to account for the known overbinding effects of the local-density approximation. The predictions were consistent with recent transient x-ray diffraction data on silicon.