Proton-proton pair distribution in dense fluid hydrogen

Recent experiments on hydrogen at very high pressures have stimulated new quantum statistical studies of this simplest Coulomb system since a transition from nonconducting to metallic behavior occurs at Mbar pressures which is forced by drastic changes of the electronic and structural properties in the molecular system with increasing density. The variation of the thermodynamic and structural properties as a function of the density and temperature can be studied within molecular dynamics and Monte Carlo simulations as well as within analytical approaches such as integral equation techniques. In the region where hydrogen molecules still dominate the physical behavior, the proton-proton pair distribution function is determined both from a modified hypernetted chain approximation which starts with effective intermolecular and interatomic potentials in the neutral system, and a wave-packet molecular dynamics simulation with the Coulomb interaction between protons and electrons as the basic interaction. Comparison of both complementary approaches gives hints for the validity region of the chemical picture as well as for the accuracy of computer simulations.