1.14*CM1A-LBCC: Localized Bond-Charge Corrected CM1A Charges for Condensed-Phase Simulations

TLDR

1.14*CM1A charges are easily obtained for large systems but show large deviations for some functional groups. The study evaluates the accuracy of 1.14*CM1A and 1.20*CM5 charge models for hydration free energy calculations. They improved the charges by applying localized bond‑charge corrections that adjust partial charges for specific bond types. The 1.14*CM1A and 1.20*CM5 models achieve mean absolute deviations of 1.26 and 1.21 kcal mol⁻¹ for hydration free energies, while the LBCC‑corrected 1.14*CM1A‑LBCC reduces the error to 0.61 kcal mol⁻¹ and gives comparable accuracy for heats of vaporization and densities.

Abstract

The quality of the 1.14*CM1A and 1.20*CM5 charge models was evaluated for calculations of free energies of hydration. For a set of 426 neutral molecules, 1.14*CM1A and 1.20*CM5 yield MADs of 1.26 and 1.21 kcal/mol, respectively. The 1.14*CM1A charges, which can be readily obtained for large systems, exhibit large deviations only for a subset of functional groups. The results for these cases were systematically improved using localized bond-charge corrections (LBCC) by which offsetting adjustments are made to the partial charges for atoms in specified bond types. Only 19 LBCCs were needed to yield 1.14*CM1A-LBCC charges that reduce the errors for the 426 ΔGhyd values to only 0.61 kcal/mol. The modified charge method was also tested in computation of heats of vaporization and densities for pure organic liquids, yielding average errors of 1.40 kcal/mol and 0.024 g/cm3, similar to those for 1.14*CM1A.