| Abstract: | The configuration interaction method where a single reference state is composed of a linear combination of reference configurations is analyzed in detail. In this method single and double replacements are constructed by applying annihilation and creation operators on the reference state. The analysis is based on the recently derived factorization of the direct CI coupling coefficients into internal and external parts. Using the internal coupling coefficients the integrals are transformed to new entities which are used in the diagonalization step. This two-step procedure differs significantly from the usual straightforward one-step direct CI procedure. A number of operations analysis shows that calculations with the present method should be feasible even with a large number of reference configurations in the reference state. Based on first-order perturbation theory the accuracy of the method is predicted to be close to the accuracy obtained with the usual CI method with many reference configurations. |
