Wave packet molecular dynamics simulations of hydrogen under extreme conditions

Abstract
With the aid of "Wave Packet Molecular Dynamics" (WPMD) simulations we investigate hydrogen under extreme conditions. In this model the protons are treated as classical point-particles, whereas the electrons follow a pseudo-hamiltonian dynamics. For the simulations we use up to 4000 particles in a periodically continued cubic box. The equation of state, i.e. the pressure as function of the temperature for an electron density n = 2. 10²⁹m^-3 is rather flat between 5000 K and 12000 K. In this regime the molecules dissociate. Above 20000 K we observe another structure in p(T), which is associated with ionization. The linear mixing model shows a similar behaviour of the pressure, but at lower absolute values. The PIMC treatment seems to overestimate 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 peak and pronounced long-range correlations. This indicates a molecular crystal which can indeed be verified by inspecting the particle positions.