Water on BN doped benzene: A hard test for exchange-correlation functionals and the impact of exact exchange on weak binding

TL;DR

This study investigates how the inclusion of exact exchange in density functional theory affects the prediction of water's binding orientation on doped benzene derivatives, emphasizing the importance of exchange and dispersion effects for accurate modeling.

Contribution

It demonstrates that high exact exchange proportions are crucial for correct water binding orientations on doped aromatic surfaces, highlighting the need for combined exchange and dispersion functionals.

Findings

Lack of exact exchange predicts incorrect water orientation.

High exact exchange improves binding conformation predictions.

Non-local van der Waals functionals accurately estimate interaction energies.

Abstract

Density functional theory (DFT) studies of weakly interacting complexes have recently focused on the importance of van der Waals dispersion forces whereas, the role of exchange has received far less attention. Here, by exploiting the subtle binding between water and a boron and nitrogen doped benzene derivative (1,2-azaborine) we show how exact exchange can alter the binding conformation within a complex. Benchmark values have been calculated for three orientations of the water monomer on 1,2-azaborine from explicitly correlated quantum chemical methods, and we have also used diffusion quantum Monte Carlo. For a host of popular DFT exchange-correlation functionals we show that the lack of exact exchange leads to the wrong lowest energy orientation of water on 1,2-azaborine. As such, we suggest that a high proportion of exact exchange and the associated improvement in the electronic structure could be needed for the accurate prediction of physisorption sites on doped surfaces and in complex organic molecules. Meanwhile to predict correct absolute interaction energies an accurate description of exchange needs to be augmented by dispersion inclusive functionals, and certain non-local van der Waals functionals (optB88- and optB86b-vdW) perform very well for absolute interaction energies. Through a comparison with water on benzene and borazine (B$_3$N$_3$H$_6$) we show that these results could have implications for the interaction of water with doped graphene surfaces, and suggest a possible way of tuning the interaction energy.