Wave packet molecular dynamics simulations of hydrogen under extreme conditions

With the aid of "Wave Packet Molecular Dynamics" (WPMD) simulations we inve stigate hydrogen under extreme conditions. In this model the protons are tr eated as classical point-particles, whereas the electrons follow a pseudo-h amiltonian dynamics. For the simulations we use up to 4000 particles in a p eriodically continued cubic box. The equation of state, i.e. the pressure a s function of the temperature for an electron density n = 2.10(29)m(-3) is rather fiat between 5000 K and 12000 K. In this regime the molecules dissoc iate. Above 20000 K we observe another structure in p(T), which is associat ed with ionization. The linear mixing model shows a similar behaviour of th e pressure, but at lower absolute values. The PIMC treatment seems to overe stimate the effect of dissociation, while the tight-binding model shows no structure at all. Independent structure information is obtained from proton pair correlation functions. Below 500 K we observe a dominant molecular pe ak and pronounced long-range correlations. This indicates a molecular cryst al which can indeed be verified by inspecting the particle positions.