Configuration interaction calculations of the helium pair potential including CI superposition corrections

Configuration interaction calculations, involving all single and double excitations, are used to calculate the He2 potential as a test of a method of calculating the CI basis superposition error. The method is also investigated using model calculations with a limited basis. For the main He2 calculations a gaussian basis (5s, 3p, 2d) is employed. This basis includes functions appropriate to the description of both intra and interatomic correlation. The effect of various changes in the basis and the effect of the addition of f orbitals is investigated. Qualitative agreement with earlier calculations which avoided the superposition error is obtained.