Potential-Energy Curves for the Ground and Several Electronic States of NdO and NdS

Potential energy curves (PECs) were calculated for 21 and 18 electronic states of NdO and NdS molecules, respectively. In each case, static electron correlation effects were described by incomplete model space multiconfiguration self-consistent field wave functions based on an active space that included the most important valence orbitals. Dynamic electron correlation was included by the multireference second-order generalized Van Vleck perturbation theory method. Scalar-relativistic contributions were included by the effective core potential approach, using def2-TZVPP basis sets. Spin-dependent relativistic corrections were determined to be small and negligible for the Nd atom and so were not included in the calculations. The 21 and 18 electronic states of NdO and NdS were predicted to be in the excitation energy range of ∼3.2 and ∼2.7 eV, respectively. The ground electronic states of NdO and NdS were determined as 1⁵H (6s4f_σ4f_ϕ4f_δ) and 1⁵H (4f_ϕ4f_π4f_π6s), with spectroscopic constants: bond length R_e = 1.780 and 2.325 Å, and harmonic frequency ω_e = 891 and 538 cm^-1, respectively.