Nonadditive Interaction in Molecular Hydrogen at High Pressure

Abstract

Ab initio quantum-mechanical calculations have been carried out for the pair and triplet potential energies of hydrogen molecules in order to check the pairwise additivity assumption in interpreting the shock experiments of van Thiel et al. It is shown that this assumption fails at distances less than 4.5 bohr. An effective pair potential obtained from the present calculations compares favorably with experimentally determined pair potentials at 3.5 bohr or larger. At shorter distances, it shows the presence of higherorder many-body forces.