Theoretical studies of the optical spectrum band positions and spin-Hamiltonian parameters for VO2+ ions in MgNH4PO6.6H2O crystal from three microscopic methods

The optical spectrum band positions and spin-Hamiltonian parameters (g factors gparallel, gperpendicular and hyperfine structure constants Aparallel , Aperpendicular) for VO2+ ions in MgNH4PO6.6H2O crystal are calculated from three microscopic theoretical methods, namely, two complete diagonalization (of energy matrix) methods (CDM-I and CDM-II) and the perturbation theory method (PTM). In CDM-I, the Hamiltonian related to energy matrix does not contain the Zeeman interaction term and the energy matrix is established from the weak-field basis functions; while in CDM-II, the Hamiltonian includes the Zeeman interaction term and the energy matrix is established from the strong-field basis functions. The calculated results from the three methods are not only very close to one another, but also in keeping with the experimental values. This suggests that the three microscopic methods can be applied to the theoretical studies of optical and EPR spectral data for 3d1 (or some other 3dn) ions in crystals