New Relativistic Atomic Natural Orbital Basis Sets for Lanthanide Atoms with Applications to the Ce Diatom and LuF3

New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide atoms La-Lu. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies and some excitation energies. Computed ionization energies have an accuracy better than 0.1 eV in most cases. Two molecular applications are inluded as illustration: the cerium diatom and the LuF3 molecule. In both cases it is shown that 4f orbitals are not involved in the chemical bond in contrast to an earlier claim for the latter molecule.Swedish Research CouncilSwedish Research CouncilLinnaeus Center of Excellence on Organizing Molecular Matter (OMM)Linnaeus Center of Excellence on Organizing Molecular Matter (OMM)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq (Conselho Nacional de Desenvolvimento Cientifico e Teconologico, Brazil)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP (Fundacao de Amparo A Pesquisa do Estado de Sao Paulo)Laboratorio de Computacao Cientifica Avancada (LCCA)Laboratorio de Computacao Cientifica Avancada (LCCA)Universidade de Sao Paulo (USP)[FAPESP 2004/08928-3]Universidade de Sao Paulo (USP