Torsional Potentials of Glyoxal, Oxalyl Halides, and Their Thiocarbonyl Derivatives: Challenges for Popular Density Functional Approximations

The reliability of popular density
functionals was studied for
the description of torsional profiles of 36 molecules: glyoxal, oxalyl
halides, and their thiocarbonyl derivatives. HF and 18 functionals
of varying complexity, from local density to range-separated hybrid
approximations and double-hybrid, have been considered and benchmarked
against CCSD­(T)-level rotational profiles. For molecules containing
heavy halogens, most functionals fail to reproduce barrier heights
accurately and a number of functionals introduce spurious minima.
Dispersion corrections show no improvement. Calibrated torsion-corrected
atom-centered potentials rectify the shortcomings of PBE and also
improve on σ-hole based intermolecular binding in dimers and
crystals.