A Quasirelativistic Perturbation Theory As a Tool for Modeling f–f and f–d Transitions in Lanthanide Ions

Abstract The reliability of the scheme for modeling electronic transitions in lanthanide ions using uncontracted versions of quasidegenerate multireference second-order perturbation theory has been investigated. The scheme involves describing electronic subsystems using the model of generalized relativistic pseudopotentials for “small” atomic cores. Quantitative estimates of the transition energies within the 4f shell can be obtained with a model space that includes only the distributions of “active” electrons over the 4f and 5d orbitals, while further expansion of the model space is necessary to reproduce the characteristics of the f–d transitions. Due to a combination of the high accuracy and efficiency, the proposed scheme can be recommended for calculating the characteristics of localized electronic excitations in lanthanide ions on solid materials using appropriate embedded cluster models and the technique of “compound-tunable” embedding potentials.