Showing papers by "Poul Jo published in 1980"

Transition moments and dynamic polarizabilities in a second order polarization propagator approach

Abstract: We have formulated a polarization propagator approach which yields excitation energies, transition moments, and dynamic polarizabilities which are consistent through second order in the electronic repulsion. Certain terms are proven to be missing in our previous second order calculations of transition moments and dynamic polarizabilities and in the equation‐of‐motion calculations of the same quantities. Numerical calculations on carbon monoxide are performed. The calculations show that the major difference between the polarizability (and some transition moments) in the RPA and in the second order polarization propagator approximation is due to these terms. The total effect of all correction terms has been to improve considerably the agreement between theoretical and experimental estimates of the excitation properties for carbon monoxide.

Mode damping in multiconfigurational Hartree–Fock procedures

Abstract: Mode damping techniques that allow a controlled ’’walk’’ on the energy hypersurface both within the orbital and the configuration space are introduced. The use of these techniques is particularly crucial in cases where there is strong coupling between the orbital and the configuration space, e.g., the second 1Σ+g state of C2. The mode damping technique allows us to use a set of single configuration Hartree–Fock orbitals as an initial guess of orbitals and then coverge in very few iterations.

A method to reduce the number of two electron integral transformations in a second order multiconfigurational Hartree–Fock procedure

Abstract: In standard multiconfigurational Hartree–Fock (MCSCF) theory, a two electron integral transformation is performed before application of the equation defining the MCSCF approach in each iterative cycle. It is shown how the two electron integral transformation may be replaced by an approximate orbital transformation introduced directly into the equation that defines the second order MCSCF approach. In this way, the number of two electron integral transformations required to obtain a set of MCSCF orbitals is reduced considerably. Numerical examples for the 3Σ−g, 1Δg, and 1Σ+g states of O2 indicate that an accuracy of 10−6 a.u. in the total energy may be obtained by carrying out 2–3 two electron integral transformations, which is about half the number of transformations required to obtain the same accuracy in the second order MCSCF approach. An accuracy of 10−10 a.u. is obtained after one further iteration is carried out with a second order MCSCF scheme.