In this paper we present the theory and implementation of the spin–orbit coupling and Zeeman operators in the context of quasi-degenerate perturbation theory into the general spin restricted open-shell configuration interaction singles method. The implementation of the mentioned operators allows for the calculation of magnetic circularly polarized dichroism (MCD), L-edge X-ray absorption spectra (XAS) and X-ray magnetic circularly polarized dichroism (XMCD) spectra. The method was tested on calculating the MCD spectra of isostructural complexes LCrIII(PyA)3NiII2+, LCrIII(PyA)3ZnII2+and LGaIII(PyA)3NiII2+, with L = 1,4,7-trimethyl-1,4,7-triazacyclonanane and PyA– is the monoanion of pyridine-2-aldozime, where it correctly predicts the MCD signs of the lower optical transition of LCrIII(PyA)3NiII2+and LGaIII(PyA)3NiII2+. The capabilities of the method in computing L-edge XAS and XMCD spectra were tested on the model complexes Cu(H2O)62+ and Cu2(OAc)4(H2O)2, where it correctly calculates the L2,3-edge absorption and XMCD spectra, as well as on the antiferromagnetically coupled Cu–Fe dimer (F8TPP)Fe(μ-O)Cu(TMPA)+, where it correctly predicts the signs of the L2 and L3 edges of the Cu XMCD spectrum. To further illustrate the applicability of the method, the more complex L2,3-edge XAS and XMCD spectra of thiolate Fe complexes were also calculated.
Gouveia et al. (Tue,) studied this question.