Knowledge Bank

The currently most effective method of treating the electronic structure of molecules containing heavy atoms is to use effective core potentials and spinorbit operators derived from relativistic atomic calculations (M. Krauss and W. J. Stevens, Ann, Rev. Phys. Chem., 1984; P. A. Christiansen, W. C. Ermler, and K. S. Pitzer, ibid, 1985), as has been demonstrated on a large number of diatomic molecules. We have re-expressed the spin-oribit operator in a simpler form, and have written computer programs both to evaluate integrals of this operator over Gaussian atomic orbitals and to transform them to integrals over molecular obitals for polyatomic molecules. First-order perturbation theory is inadequate to treat the spin-orbit interaction for heavy atoms, so both the electron-repulsion and spin-orbit matrix elements are included in the CI (configuration interaction) matrix. The CI wavefunctions are intrinsically complex, but with minimal spatial symmetry the CI matrix can be changed to a completely real from. We have written computer programs to do these calculations using $C2v,D2$, or $D2h$ double-group symmetry. Results will be presented for the $5f\to 5f$ states of $PuF6$, and comparisons will be presented with matrix spectra and other types of calculations.