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

• The choice of atomic charges is crucial in modeling adsorption and diffusion in MOFs.
• Methods for calculating atomic charges in MOFs are reviewed.
• We discuss the influence of the framework geometry on the calculated charges.
• We discuss the influence of the framework charges on structural the properties.

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 electronic wavefunction or the electronic density or the system, as obtained with quantum mechanics 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 of IRMOF-1.

We review the different method with which to calculate atomic partial charges that can be used in force field-based calculations. We also present two examples that illustrate the influence of the geometry on the calculated charges and the influence of the charges on structural properties.Figure optionsDownload as PowerPoint slide