Density functional studies of AnF₆ (An = U, Np, and Pu) and UF_6-nCl_n (n = 1-6) using hybrid functionals: Geometries and vibrational frequencies

We have compared the performance of widely used hybrid functional for calculating the bond lengths and harmonic vibrational frequencies of AnF₆ (An = U, Np, and Pu) and UF_6-nCl_n (n = 1-6) molecules using "small-core" relativistic effective core potentials and extended basis sets. The calculated spectroscopic constants compare favorably with experimental data for the bond lengths (average error < 0.01 Å) and vibrational frequencies (average error ≤ 7 cm^-1) of the AnF₆ molecules. The experimental vibrational frequencies of the stretching modes were available for most of the UF_6-nCl_n (n = 1-6) molecules. The calculated vibrational frequencies are in good agreement with the experimental data to within 4.6 cm^-1 and 7.6 cm^-1 for selected Beckel and Lee, Yang, Parr (B1LYP), and Becke3 and Perdew, Wang (B3PW91) functionals, respectively. We conclude that one can predict reliable geometries and vibrational frequencies for the unknown related systems using hybrid density functional calculations with the RECPs. The geometries and vibrational frequencies of the UF_6-nCl_n (n = 1-6) molecules that have not been determined experimentally are also presented and discussed.