A quadratically convergent Hartree—Fock (QC-SCF) method. Application to closed shell systems

Using CI formalism the theory of a quadratically convergent Hartree—Fock method is developed which is shown to be a simple extension of single excitation CI and closely related to coupled Hartree-Fock perturbation theory. A computationally efficient practical scheme is proposed in which the costly four-index transformation step inherent in CI methods is avoided. Test calculations for the H2O, CO, C2H2N+ systems and for N2 perturbed by a finite electric field indicate that the current scheme is significantly more efficient than the widely used conventional Hartree—Fock method and is especially useful in coupled Hartree—Fock and finite field perturbation calculations.