Singlet calculations were carried out in a spin-restricted formalism while calculations of all other spin states were performed in an unrestricted formalism. Level shifting 105 of 0.25 Ha was applied to both majority-and minority-spin virtual orbitals to aid self-consistent field (SCF) convergence to an unrestricted solution. Geometry optimizations were carried out with the translation rotation internal coordinate (TRIC) optimizer 106 using the BFGS algorithm with default convergence thresholds of maximum energy gradient of 4.5 ´ 10 -4 hartree/bohr and energy difference between steps of 10 -6 hartree.