A numerical method for computing dispersion constants
Résumé
We reformulate and discuss a previously proposed variational numerical technique for the computation of dispersion coefficients. The method extends the Full CI idea to the perturbation equation for the intermolecular interaction, by expanding the perturbative solution in a small number of tensor products of suitably chosen Full CI vectors. Some new expansion vectors are proposed and their convergence properties are tested by performing computations on HF and H2O. Last, a natural state analysis of the solution is performed via an orthogonal transformation of the original expansion vectors and it is found that a single couple of natural states strongly dominates the expansion.