Finding the best density functionals for water: benchmarking the forces

TL;DR

This study benchmarks over 50 density functionals for water to identify those providing the most accurate force calculations, crucial for reliable water simulations across various phases.

Contribution

It provides a comprehensive benchmark of water force accuracy for a wide range of density functionals, highlighting the best performers and potential improvements.

Findings

B97M-V, ωB97M-V, and revDOD-PBEP86-D4 are the top functionals at different levels.

No satisfactory GGA functionals were found; a correction to BLYP-D4 improves its accuracy.

Force-based benchmarking offers better structural coverage and confidence than traditional methods.

Abstract

A DFT benchmark on water including more than 50 functionals from GGA to double-hybrid levels is reported. The main metric is the accuracy of forces, allowing better structural coverage, higher statistical confidence, and fewer error sources compared to conventional benchmarks. The input structures include water clusters of 4~128 molecules, with highly varied yet realistic configurations of water, ice, and their mixtures. The B97M-V, {\omega}B97M-V, and revDOD-PBEP86-D4 functionals are found to be best on the mGGA, hybrid, and double-hybrid levels, respectively. No satisfying GGA functionals are found, but it can be obtained by combining BLYP-D4 with a simple correction to O-H bonds, achieving accuracy comparable to B97M-V.