Performance of the bond capacity model for charge polarization in classical molecular dynamics

This study investigates the performance of force field models employing only atomic charges to model the electrostatic interactions and only charge-flow to model the electric polarization. The atomic charges and charge-flow parameters are calculated directly by ab initio methods. The performance for liquid-state properties of models that include 1-bond, 2-bond, and 3-bond charge-flow is probed for chloroform and acetonitrile through measurements of dielectric constants, dipole moments, and infrared spectra. The results indicate that models allowing charge-flow only between directly bonded atom pairs (1-bond) lead to significant deviations compared to models incorporating 2- and 3-bond contributions, suggesting that restricting charge-flow solely between directly bonded atom pairs omits important physical contributions. In addition, modeling polarizability via charge-flow inherently leads to an anisotropy description of the molecular polarizability tensor, with the level of anisotropy constituting a major component in the electrostatic response. The results also suggest that modeling the molecular polarizability by only charge-flow tends to overestimate the electric polarization and, thus, indicate that combinations of rank-0 and rank-1 polarizability are required for an accurate modeling of the electric response.