Wave Packet Simulation of Warm Dense Hydrogen

We have extended previous formulations of the wavepacket molecular dynamics (WPMD) by implementing full antisymmetrization for the electron-electron interaction and by introducing approximate Bloch waves to account for the periodic continuation of the simulation box. The improved antisymmetrization leads to a modified volume element in the Monte-Carlo (MC) sampling which serves to limit an unphysical growth of the width of the wave packets for unbound electrons. Using this scheme we performed WPMD simulations for dense hydrogen. As a benchmark, we have compared the results with experiments [1] and competing models. The equation of state at T = 300 K agrees well with diffusion Monte-Carlo results [2] Both theoretical approaches yield somewhat higher pressures than observed in the diamond anvil experiments, which were carried out up to densities n = 0.7 ·10m. The simulation results show a transition from molecular hydrogen to a metallic phase with delocalized electrons. The transition was analyzed and confirmed by examining several observables, trend in pressure, spatial widths of electronic wavefunctions, conductivity Fig. 1, particle distributions, and pair-distribution functions. The experimental results stop presently somewhat lower than the predicted transition point near n = 0.9 · 10m. Systematic simulations for a wide range of densities and temperatures yield a clear transition curve in the p−T plane Fig. 2 with a molecular phase at low temperatures and/or pressures and a metallic state otherwise. Results from density functional calculations [3, 4, 5] lie very close to the results from WPMD. At the transition curve, there is a regime of phase transition where metallic and molecular phase can coexist at the same temperature and pressure, however at much different densities (metallic hydrogen having