Torsional potentials of glyoxal, oxalyl halides and their thiocarbonyl derivatives: Challenges for popular density functional approximations

TL;DR

This study evaluates the accuracy of various density functionals in predicting torsional profiles of specific molecules, revealing limitations with heavy halogen compounds and the effectiveness of calibrated potentials.

Contribution

It benchmarks a wide range of density functionals against high-level calculations for torsional profiles and introduces calibrated potentials to improve accuracy.

Findings

Most functionals fail for heavy halogen molecules.

Dispersion corrections do not improve results.

Calibrated potentials enhance PBE performance.

Abstract

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 \textcolor{black}{eighteen} 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, all functionals except M05-2X and M06-2X 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 $\sigma$-hole based intermolecular binding in dimers and crystals.