Zero-field splitting calculations based on semiempirical MR-CI wave functions

A method for computing the spin-dipolar coupling tensor based on semiempiri cal MNDOC-CI wave functions is described. To simulate the neglect of differ ential diatomic overlap (NDDO) approximation, Lowdin-orthogonalized Gaussia n-type orbitals (GTOs) were used to evaluate the two electron integrals ove r the spin-dependent Breit-Pauli Hamiltonian. Tests and applications of the method involve carbene, tetramethyleneethane, twisted ethylene, and ring-o pened oxirane biradical. The results provide a definition of the T-x, T-y, and T-z triplet wave functions, the set of principal magnetic molecular axe s, and the spin-spin-only values of the zero-field splitting parameters D a nd E. (C) 2000 John Wiley & Sons, Inc.