Advanced Electrostatic Model for Monovalent Ions Based on Ab Initio Energy Decomposition

Ions
play important roles in the structures and functions of biomolecules.
In biomolecular simulations, ions either directly interact with biomolecules
or provide an ionic environment that influences electrostatic interactions
of solutes. The AMOEBA+ water model has demonstrated significant advancement
of the classical force field for describing molecular interactions
due to its improvements on the functional forms to account for essential
physics. This work expands the applicability of the AMOEBA+ model
toward alkali metal (Li, Na, K, Rb, and Cs) and halogen (F, Cl, Br,
and I) ions. Various quantum chemical data on ion–ion and ion–water
interactions, experimental ion hydration free energies, and lattice
energies of salt crystals are used in the parametrization. The final
parameters are verified with other properties outside of the parametrization
data, including lattice energies of additional salt crystals and ionic
activity coefficients in solution. The new model captures a wide range
of ion properties from the gas phase to solution phase and crystals.
More importantly, AMOEBA+ provides energy components that are consistent
with ab initio energy decomposition. Thus, we expect AMOEBA+ to be
more general, transferable, and valuable for the interpretation of
intermolecular forces in efficient classical simulations.