Wave packet simulation of dense hydrogen

Abstract

Dense hydrogen is studied in the framework of wave packet molecular dynamics. In this semiquantal many-body simulation method the electrons are represented by wave packets which are suitably parametrized. The equilibrium properties and time evolution of the system are obtained with the help of a variational principle. At room temperature the results for the isotherms are in good agreement with anvil experiments. At higher densities beyond the range of the experimental data a transition from a molecular to a metallic state is predicted. The wave packets become delocalized and the electrical conductivity increases sharply. The phase diagram is calculated in a wide range of the pressure-density-temperature space. The observed transition from the molecular to metallic state is accompanied by an increase in density in agreement with recent reverberating shock wave experiments.

Evidence of maximum in the melting curve of hydrogen at megabar pressures

“…4 Ω -1 cm -1 , as calculated in [7,11,30]. We found that the drop in resistance at the point of hydrogen melting was less pronounced Fig.…”

“…A metallic-like state might appear due to narrowing of the band gap with increasing temperature [7,9,11]. Currently available experimental data are insufficient to enable us to discriminate among the above scenarios.…”

“…It is apparently related to dramatic changes in the surrounding fluid hydrogen. As soon as hydrogen melts at pressures above ~150 GPa molecules rapidly dissociate with temperature according to calculations [7,9,11]. Therefore atomic hydrogen (protons) can penetrate the bordering Pt foil causing a change of resistance; however, negligible hydrogen is dissolved in Pt (in contrast to Pd), even at 9 GPa and 520 K [28].…”

“…1: from [1] (open diamond), [6] (solid square), [9] (circles), [7] (open square), and [12] (star). See also [8,10,11]. Therefore, hydrogen might already occur in its metallic state at accessible pressures of P > 100 GPa and temperatures of below T = 2000 K (Fig.…”

Probing the Hydrogen Melting Line at High Pressures by Dynamic Compression

“…Despite its seemingly simple composition, hydrogen is known to have a variety of complex phases [1]. Moreover, both experimental [2][3][4][5][6][7][8][9] and theoretical [10][11][12][13][14][15][16] methods have so far failed to give conclusive answers concerning the existence of a plasma phase transition, the nature of the molecular to atomic transition in the high density fluid, the location of the metallization transition in the solid, the melting line for pressures higher than 250 GPa [17] and the question of a possible liquid at T = 0 K connected to it [18].…”