Multireference CI study of the potential curves and properties of positronic complexes of alkali hydrides

Ab initio multireference single- and double-excitation configuration interaction (MRD-CI) calculations have been carried out to study the manner in which the electronic structure of the series of neutral alkali hydride molecules is affected by the interaction of a lone positron. Four systems have been treated: LiH, NaH, KH and RbH. A new computer program has been constructed for this purpose that makes use of the Table-Direct-CI method for molecular calculations within the Born–Oppenheimer approximation. The main emphasis in the present work is on internuclear geometries with relatively large bond distances near the dissociation limit. Molecular charge density contour diagrams are presented to illustrate the bonding mechanism in each case. Trends in a variety of quantities such as positron affinities at both equilibrium molecular and separated atomic geometries, dissociation energies and positronium formation energies are computed and analyzed as the atomic number of the alkali atom is increased.