Core-shell potential-derived point charges

The present work details the development of a core-shell model for the purposes of obtaining potential-derived point charges from the ab initio molecular electrostatic potential. In contrast to atomic point charge models, the core-shell model decomposes all atoms into a core with static charge located at a fixed atomic position and a shell with variable charge and position. The optimization of shell charges and positions is discussed. The core-shell model was found to significantly improve description of the ab initio electrostatic potential when compared to potential-derived net atomic point charge models as well as distributed multipoles with contributions up to atomic quadrupole moments. The core-shell model was found to produce similar results as the Weller-Williams lone-pair model and differences in the implementation of the models are discussed.