Molecular open shell configuration interaction calculations using the Dirac–Coulomb Hamiltonian:The f 6‐manifold of an embedded EuO9−6 cluster

We present results of all-electron molecular relativistic (Hartree-Fock-Dirac) and nonrelativistic (Hartree-Fock) calculations followed by a complete open shell configuration interaction (COSCI) calculation on an EuO6(9-) cluster in a Ba2GdNbO6 crystal. The results include the calculated energies of a number of states derived from the f6 - manifold and 5D-7F luminescence transition wavelengths. The calculations were performed using the molecular Fock-Dirac (MOLFDIR) program package developed in our laboratory. The theory and methods employed in this package are briefly described. The physical models used to analyze the Eu3+ impurity states range from a bare Eu3+ ion to an EuO6(9-) cluster embedded in a Madelung potential representing the rest of the crystal. We show that it is necessary to use the embedded cluster model to get a reasonable description of the crystal field splittings of the states arising from the f6-manifold. Our results indicate that the calculated splittings are very sensitive to the orbitals used. It is therefore essential that relativistic orbitals be used from the outset