Parameterization of MMFF/NQEq for alcohol, ether, and carbohydrate

Abstract

Molecular simulations using the conventional force fields have been successful for understanding the nanoscopic behavior of molecules in several chemical environments. However, the classical approaches have some shortcomings due to the electrostatic interaction calculated by fixed atomic charges. To describe the charge reorganization due to nuclear structrural changes of the molecules, recently, we developed the new charge equilibration (NQEq) framework that the parameters are classified to 60 atomic types and optimized to reprduce the experimental dipole moments of several organic compounds. In this study, we presented the new force field, MMFF/NQEq, that the electrostatic energy term evaluated with fixed charges based on the bond-charge increment method in the Merck Molecular Force Field (MMFF) was replaced by the energy expression of NQEq, and that the parameter set of torsion interaction term was refined. MMFF/NQEq can reproduce the relative energies of conformational isomers of the organic compounds obtained by high-level ab initio calculations. We will discuss the accuracy and usefulness of the calculations using MMFF/NQEq.