Ground and Excited Electronic State Analysis of PrF²⁺and PmF²⁺

Abstract

The ground state and excited state manifolds are computed for PrF(2+) and PmF(2+) at the CASSCF (n,8) level of theory where the active space spans the Ln 4f orbitals as well as the F 2pz orbital. Dynamical correlation is included using second-order multireference quasidegenerate perturbation theory (MCQDPT2). The spin-orbit multiplets for each of the excited states are resolved, and spin-orbit coupling constants are computed using the Breit-Pauli spin-orbit operator. Equilibrium geometries for each of the ground and excited states are computed, and the nature of the Ln-F bond is examined. Potential energy curves for the lowest four triplet states and lowest two quintet states are computed for PrF(2+), which split into 14 levels upon application of the spin-orbit Hamiltonian. Likewise, the lowest six quintet states are computed for PmF(2+) as well as the lowest triplet state and the lowest two septet states. These nine states split into 43 terms upon application of the spin-orbit Hamiltonian.

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 .…”

Dissociation energy and electronic structure of the low valent lanthanide compound NdF+

“…Recent work on lanthanide fluorides has focused on the determination of thermochemical, geometric, and electronic properties using highly correlated and multireference ab initio methods for lanthanide complexes . NdF 2+ was examined using complete active space SCF (CASSCF) and second‐order multiconurational quasi‐degenerate perturbation theory (MCQDPT2) and was found to have a very dense set of roughly parallel electronic states, similar to that found with PrF 2+ and PmF 2+ . The observed states were the result of permutations of 4f orbital occupations that resembled the low‐lying electronic states of NdF 3 , thereby demonstrating the utility of NdF 2+ as a simplified model of the Nd‐F bond in NdF 3 Neutral NdF was analyzed using both CASSCF and equation of motion completely renormalized coupled cluster (EOM‐CR‐CCSD(T)) and was shown to possess a very different electronic structure than NdF 2+ owing to the contributions from the neodymium 5d and 6s orbitals …”

“…[18,22,23,[27][28][29][30] NdF 21 was examined using complete active space SCF (CASSCF) and second-order multiconurational quasi-degenerate perturbation theory (MCQDPT2) and was found to have a very dense set of roughly parallel electronic states, [29] similar to that found with PrF 21 and PmF 21 . [31] The observed states were the result of permutations of 4f orbital occupations that resembled the low-lying electronic states of NdF 3 , thereby demonstrating the utility of NdF 21 as a simplified model of the Nd-F bond in NdF 3 [29] Neutral NdF was analyzed using both CASSCF and equation of motion completely renormalized coupled cluster (EOM-CR-CCSD(T)) and was shown to possess a very different electronic structure than NdF 21 owing to the contributions from the neodymium 5d and 6s orbitals. [30] The current work focuses on NdF 1 , where neodymium is formally in the less common 12 oxidation state.…”

The electronic configurations of LnX (Ln=La–Eu, X=O, S, Se, Te): A FON–DFT investigation

“…Schoendorff and coworkers in 2014 calculated the radial distribution functions of Nd(4f,5s,5p) and F(2p) shells and put them at the equilibrium distance of NdF molecule [23]. Similar method was later applied to PrF 2+ and PmF 2+ and overlapping of atomic shells was observed implying possibility of 'covalent mixing' [24]. Orbital mixings of Ln(4f) have been observed in LuF 3 [25], LnF 3 (Ln = La to Lu) [26] and LnCl 6 XÀ [27], which are not evidences of bonding according to our previous discussion [26] and Pyykkö's correction [28].…”