On how good DFT exchange-correlation functionals are for H bonds in small water clusters: Benchmarks approaching the complete basis set limit

TL;DR

This study systematically evaluates the accuracy of various DFT exchange-correlation functionals in modeling hydrogen bonds in small water clusters, benchmarking against high-level MP2 calculations with minimized basis set errors.

Contribution

It provides a comprehensive benchmark of DFT functionals for water clusters, highlighting the best performers and their limitations in describing hydrogen bonds.

Findings

Hybrid X3LYP and PBE0 perform best among tested functionals.

Non-hybrid mPWLYP and PBE1W show strong performance.

BLYP and B3LYP tend to underbind water clusters.

Abstract

The ability of several density-functional theory (DFT) exchange-correlation functionals to describe hydrogen bonds in small water clusters (dimer to pentamer) in their global minimum energy structures is evaluated with reference to second order Moeller Plesset perturbation theory (MP2). Errors from basis set incompleteness have been minimized in both the MP2 reference data and the DFT calculations, thus enabling a consistent systematic evaluation of the true performance of the tested functionals. Among all the functionals considered, the hybrid X3LYP and PBE0 functionals offer the best performance and among the non-hybrid GGA functionals mPWLYP and PBE1W perform the best. The popular BLYP and B3LYP functionals consistently underbind and PBE and PW91 display rather variable performance with cluster size.