Benchmark tests of a strongly constrained semilocal functional with a long-range dispersion correction

TL;DR

This paper evaluates a strongly constrained meta-GGA density functional, SCAN, combined with a dispersion correction, demonstrating significant improvements in accuracy for molecular geometries, lattice energies, and thermochemistry over other methods.

Contribution

The study introduces an effective dispersion correction to the SCAN functional, significantly enhancing its performance for various molecular and solid-state properties.

Findings

Lattice energies of organic crystals improved by 50% with dispersion correction.

Meta-GGA with dispersion correction achieves sub-picometer accuracy in bond lengths.

Weighted mean absolute deviation for thermochemistry below 4 kcal/mol.

Abstract

The strongly constrained and appropriately normed (SCAN) semilocal density functional [J. Sun, A. Ruzsinszky, J. P. Perdew \textit{Phys. Rev. Lett.} {\bf 115}, 036402 (2015)] obeys all 17 known exact constraints for meta-generalized-gradient approximations (meta-GGA) and includes some medium range correlation effects. Long-range London dispersion interactions are still missing, but can be accounted for via an appropriate correction scheme. In this study, we combine SCAN with an efficient London dispersion correction and show that lattice energies of simple organic crystals can be improved with the applied correction by 50\%. The London-dispersion corrected SCAN meta-GGA outperforms all other tested London-dispersion corrected meta-GGAs for molecular geometries. Our new method delivers mean absolute deviations (MADs) for main group bond lengths that are consistently below 1\,pm, rotational constants with MADs of 0.2\%, and noncovalent distances with MADs below 1\%. For a large database of general main group thermochemistry and kinetics, it also delivers a weighted mean absolute deviation below 4 kcal/mol, one of the lowest for long-range corrected meta-GGA functionals. We also discuss some consequences of numerical sensitivity encountered for meta-GGAs.