Selenium chemistry with DFT:: molecular structures and 77Se NMR shielding constants

Optimized geometries of fourteen selenium-containing molecules are determined using density functional theory, with the VT3, HCTH and OLYP generalized gradient approximations and the B3LYP and B97-2 hybrid functionals. Bond length quality can be summarized as B97-2 > KT3 > B3LYP > HCTH > OLYP. For a subset of seven molecules, the same functionals are used to determine isotropic and anisotropic shielding constants. The shielding quality can be summarized as KT3 > B97-2 > HCTH approximate to OLYP > B3LYP. The study supports earlier observations that, by DFT standards, KT3 can simultaneously provide good quality geometries and shielding constants, without the inclusion of exact exchange. The study also highlights the relatively poor results from the widely-used B3LYP functional.