A Neoteric Neodymium Model: Ground and Excited Electronic State Analysis of NdF²⁺

Abstract

Neodymium monofluoride dication was studied as a model of the Nd-F bond in NdFx. Multiconfigurational self-consistent field (MCSCF) and second order multireference quasi-degenerate perturbation theory (MCQDPT2) methods were used with a variety of active spaces to elucidate the roles of the Nd 4f, 5d, and 6s orbitals. Spin-orbit coupling calculations were performed at the SO-MCQDPT2 level, and potential energy curves were obtained for the four lowest energy quartet states as well as for the four lowest doublet states and the lowest sextet state. Inclusion of spin-orbit coupling splits these states into 30 levels. Equilibrium bond lengths, dissociation energies, transition energies, and crossing points were determined.

Low valency in lanthanides: A theoretical study of NdF and LuF

“…The degenerate 4 B 1 and 4 B 2 states comprise the 4 state in C ∞v symmetry, and the degenerate 6 B 1 and 6 B 2 states comprise the 6 state in C ∞v symmetry. Contrary to the NdF 2+ case where Nd is in the common +3 oxidation state, 36 the PECs for the neutral species with Nd formally in the +1 oxidation state are not parallel. In general, the quartet state minima are generally at slightly shorter internuclear distances than the sextet state minima.…”

Efficacy of Density Functionals and Relativistic Effective Core Potentials for Lanthanide-Containing Species: The Ln54 Molecule Set

“…For example, the low-lying excited states of NdF have been shown to have multiple crossing points with the ground state near the equilibrium geometry . DFT approaches are largely implemented as single-reference methods, and in molecules like NdF it is very likely that DFT calculations may converge to one of the low-lying excited states rather than to the ground state . This problem can be alleviated by using multireference methods such as complete active space self-consistent field method (CASSCF), but multireference methods usually scale combinatorially with the size of the active space making them generally more computationally demanding than many wave function based single reference approaches.…”

Gauging the Performance of Density Functionals for Lanthanide-Containing Molecules

“…This is due primarily to the partial occupation of the 4 f shell that dominates the multireference character of lanthanides in the common 3+ oxidation state. Yet the pseudo-core-like nature of the 4 f orbitals results primarily in ionic bonding with excited state surfaces that tend to be parallel to the ground state. , In addition to the 4 f degeneracy, lanthanides in low-valency states also have near degeneracies between the 6 s and 5 d shells. Occupation of the 6 s and 5 d shells tends to result in covalent bonding, and the difference in the radial extent of the 6 s and 5 d orbitals leads to excited states surfaces that are not parallel to the ground state and hence numerous surface crossings occur .…”