Charge Equilibration Based on Atomic Ionization in Metal–Organic Frameworks

In this article, two new charge equilibration methods for estimating atomic partial charges are outlined. These methods are based on expanding the Taylor series used to estimate the ionization energy of each atom about either the formal or atomic charge, allowing for accurate charge estimation in both covalent and ionic materials. A new treatment of hydrogen atoms based on molecular hydrogen is also introduced. To demonstrate their general applicability, these new methods have been applied to the simulation of CO2 adsorption in metal–organic frameworks. Comparisons with other charge equilibration methods and density functional theory (DFT) calculations show that, of the rapid charge-assigning methods, the algorithm based on atomic ionization best replicates the DFT electrostatic potential and provides the most accurate estimation of CO2 adsorption.