The Fast CI Method for Second-Order Properties

Second-order properties are computed by diagonalizing a perturbed hamiltonian in a linear space L of low dimensionality. The choice of the basis vectors generating L is suggested by perturbation theory and previous work on correlation energy. Diagrammatic techniques can be used to compute the relevant matrix elements. Test numerical computations performed on the hydrogen molecule gave satisfactory results for the dipole polarizability and nuclear spin-spin coupling constant.