Intermolecular diatomic energies of a hydrogen dimer with non-Born–Oppenheimer nuclear and electron wave packets

We have developed an efficient theoretical framework of a non-Born–Oppenheimer (non-BO) nuclear and electron wave packet (NWP and EWP) method and applied it to intra- and intermolecular energies of a hydrogen dimer. The energy surface functions were derived at low computational cost. In contrast with the ordinary BO nuclear quantization on a given energy surface that reduces the effective barrier, non-trivial non-BO interactions between the EWPs and NWPs resulted in increases of intermolecular rotational and translational barriers. A direct comparison demonstrated that the non-BO effect on the intermolecular energy is significant.