Application of magnetically perturbed time-dependent density functional theory to magnetic circular dichroism. II. Calculation of A terms.

The magnetically perturbed time-dependent density functional theory is used to derive equations for the magnetic circular dichroism (MCD) of degenerate transitions of closed shell molecules. The MCD of this type of transition can be divided into two contributions. The dominant contribution is usually that from A terms that arise because of the breaking of the degeneracy of the excited state in the presence of the magnetic field. The second contribution comes from B terms that arise because of the perturbation of the transition dipole by the magnetic field. The formalism is applied to ten tetrahedral d(0) transition metal oxy- and thioanions. The MCD parameters of these systems are reproduced quite well by the calculations. Simulated spectra derived from the calculated parameters are in good agreement with the observed spectra.