Ab initio investigation of helium bubble formation from trapped He⁺ ions in solid hydrogen

We are involved in a program aimed at a first-principles examination of the possibility of helium bubble formation in solid hydrogen. Our procedure is based on an extension of the Hartree-Fock cluster approach that we have been using for study of individual He⁺ ions in solid hydrogen. The preliminary results of our cluster investigations of a particular configuration of two He⁺ ions in neighboring tetrahedral interstitial positions are presented here. It has been found that the hydrogen molecules common to the two He⁺ ions lead to a substantial attractive force between the ions that almost overcomes their inherent repulsion, leading to a binding energy for this configuration only slightly less than the binding energy for two well separated trapped He⁺ ions. The analysis of our results have suggested future investigations of different pairs of trapping sites which appear to be more favorable for providing higher binding energies for the He⁺ pairs.