Molecular formation and electron correlation in HeH +

A one‐centre CI wave function for HeH + reported by Stuart and Matsen for 0.1 ⩽ R ⩽ 5.0 has been analysed in detail from the viewpoint of molecular formation. Further, by means of a natural orbital analysis, it was possible to obtain some measure of the electron correlation contained within such wave functions for various R values. These effects were illustrated by means of a series of difference maps for the electron density. One‐ and two‐particle expectation values were obtained as a function of R . Thus, it was possible to study several aspects of the influence of the proton on the electron charge cloud as we pass from He through to the united atom Li + . The occupation numbers within the natural expansions were compared with those which arise from a similar analysis of a two‐centre wave function for HeH + . The “character” of such wave functions for HeH + , and also for He and Li + , were analysed and compared.