One class of the problems where the spin-orbit interaction becomes interesting involves spin-forbidden transitions between singlet and triplet states, responsible for the long lifetime of phosphorescent states. The singlet-triplet transition moments are evaluated as the residues of quadratic response functions. This has been accomplished through the use of modest-size MCSCF wave function. We investigate the performance of an atomic mean-field approximation to the spin-orbit interaction Hamiltonian in calculations of phosphorescence radiative lifetimes for selected organic molecules with external and internal perturbers. A comparison of the performance of the mean-field approximation with the full spin-orbit operator is also made. As we progress down in periodic table, for heavy systems we take into account scalar relativistic effects using one-electron Douglas-Kroll integral corrections. The mean-field approximation is shown to give excellent results compared=2Eto calculations with the full one- and two-electron spin-orbit integrals=2Eand significantly reduces the disk space requirements and computational cost. MNF SO approximation demonstrates the ability in estimating spin-orbit matrix elements and is a powerful approach to spin-orbit induced properties in ab initio calculations of large systems.

One class of the problems where the spin-orbit interaction becomes interesting involves spin-forbidden transitions between singlet and triplet states, responsible for the long lifetime of phosphorescent states. The singlet-triplet transition moments are evaluated as the residues of quadratic response functions. This has been accomplished through the use of modest-size MCSCF wave function. We investigate the performance of an atomic mean-field approximation to the spin-orbit interaction Hamiltonian in calculations of phosphorescence radiative lifetimes for selected organic molecules with external and internal perturbers. A comparison of the performance of the mean-field approximation with the full spin-orbit operator is also made. As we progress down in periodic table, for heavy systems we take into account scalar relativistic effects using one-electron Douglas-Kroll integral corrections. The mean-field approximation is shown to give excellent results compared=2Eto calculations with the full one- and two-electron spin-orbit integrals=2Eand significantly reduces the disk space requirements and computational cost. MNF SO approximation demonstrates the ability in estimating spin-orbit matrix elements and is a powerful approach to spin-orbit induced properties in ab initio calculations of large systems.