# Explicit treatment of hydrogen bonds in the Universal Force Field: validation and application for Metal-Organic Frameworks, hydrates and host-guest complexes

## TL;DR

This paper introduces an explicit hydrogen bond treatment within the Universal Force Field, improving accuracy in modeling hydrogen-bonded systems like metal-organic frameworks and hydrates, and enabling faster, more reliable computational analyses.

## Contribution

The authors develop and validate a new explicit hydrogen bond approach in UFF, enhancing structural prediction accuracy for complex hydrogen-bonded systems without arbitrary charge assignment.

## Key findings

- Reduces maximum error in cell parameters from 66% to 14%.
- Decreases mean unsigned error from 14% to 4%.
- Enables rapid and accurate modeling of hydrogen-bonded frameworks.

## Abstract

A straightforward means to include explicit hydrogen bonds within the Universal Force Field is presented. Instead of treating hydrogen bonds as non-bonded interaction subjected to electrostatic and Lennard-Jones potentials, we introduce an explicit bond with negligible bond order, thus maintaining the structural integrity of the H-bonded complexes and avoiding the necessity to assign arbitrary charges to the system. The explicit hydrogen bond changes the coordination number of the acceptor site and the approach is thus most suitable for systems with under-coordinated atoms, such as many metal-organic frameworks, however, it also shows excellent performance for other systems involving a hydrogen-bonded framework. In particular, it is an excellent means for creating starting structures for molecular dynamics and for investigations employing more sophisticated methods. The approach is validated for the hydrogen bonded complexes in the S22 dataset and then employed for a set of metal-organic frameworks from the Computation-Ready Experimental (CoRE) database and several hydrogen bonded crystals including water ice and clathrates. We show that direct inclusion of hydrogen bonds reduces the maximum error in predicted cell parameters from 66% to only 14% and the mean unsigned error is similarly reduced from 14% to only 4%. We posit that with the inclusion of hydrogen bonding, the solvent-mediated breathing of frameworks such as MIL-53 is now accessible to rapid UFF calculations, which will further the aim of rapid computational scanning of metal-organic frameworks while providing better starting points for electronic structure calculations.