# Hydrogen Bond Benchmark: Focal‐Point Analysis and Assessment of DFT Functionals

## TL;DR

This paper benchmarks hydrogen bond energies using advanced computational methods and finds the best-performing functionals for accuracy and efficiency.

## Contribution

A new hierarchical ab initio benchmark and evaluation of 60 DFT functionals for hydrogen bond accuracy in various systems.

## Key findings

- Meta-hybrid M06-2X performs best for hydrogen bond energies and geometries.
- Dispersion-corrected GGAs BLYP-D3(BJ) and BLYP-D4 offer accurate and cost-effective alternatives.
- Focal point analyses converge hydrogen-bond energies within tenths of a kcal mol−1.

## Abstract

We performed a hierarchical, convergent ab initio benchmark study and systematically analyzed the performance of density functional approximations for describing hydrogen bonds in small neutral, cationic, and anionic complexes, as well as in larger systems involving amide, urea, deltamide, and squaramide moieties. Focal point analyses (FPA), extrapolating to the ab initio limit, were carried out using correlated wave function methods up to CCSDT(Q) for the small complexes and CCSD(T) for the larger systems, together with correlation‐consistent Gaussian basis sets up to the complete basis set limit. Optimized geometries and vibrational frequencies were obtained at the CCSD(T) level. The resulting FPA hydrogen‐bond energies converge within a few tenths of a kcal mol−1. These reference data were used to evaluate 60 density functionals (including 12 dispersion‐corrected), spanning the local‐density approximation (LDA), generalized gradient approximations (GGAs), meta‐GGAs, hybrids, meta‐hybrids, double‐hybrids, and range‐separated hybrids. Overall, the meta‐hybrid M06‐2X provides the best performance for both hydrogen bond energies and geometries, while the dispersion‐corrected GGAs BLYP‐D3(BJ) and BLYP‐D4 also yield accurate hydrogen‐bond data and can serve as cost‐effective options for studying large and complex systems.

Our comprehensive hierarchical ab initio benchmark up to CCSDT(Q)/CBS in combination with a DFT performance study reveals that the meta‐hybrid M06‐2X provides the best performance for both hydrogen bond energies and geometries. The dispersion‐corrected GGAs BLYP‐D3(BJ) and BLYP‐D4 also yield accurate hydrogen‐bond data and can serve as cost‐effective alternatives for studying large and complex systems.