Atomic charges for modeling metal-organic frameworks: Why and how

TL;DR

This paper reviews methods for assigning atomic partial charges in Metal-Organic Frameworks (MOFs), emphasizing their impact on simulation accuracy and illustrating effects of structural variations on charge calculations and properties.

Contribution

It provides a comprehensive overview of charge calculation methods for MOFs and analyzes how small structural changes influence atomic charges and predicted properties.

Findings

Different charge calculation methods yield varying atomic charges.

Small structural variations significantly affect atomic charges.

Atomic charge variations impact the predicted structural properties of MOFs.

Abstract

Atomic partial charges are parameters of key importance in the simulation of Metal-Organic Frameworks (MOFs), since Coulombic interactions decrease with the distance more slowly than van der Waals interactions. But despite its relevance, there is no method to unambiguously assign charges to each atom, since atomic charges are not quantum observables. There are several methods that allow the calculation of atomic charges, most of them starting from the wavefunction or the electronic density or the system, as obtained with quantum mechanical calculations. In this work, we describe the most common methods employed to calculate atomic charges in MOFs. In order to show the influence that even small variations of structure have on atomic charges, we present the results that we obtained for DMOF-1. We also discuss the effect that small variations of atomic charges have on the predicted structural properties IRMOF-1.