Fast, efficient generation of high-quality atomic charges

The novel AM1-BCC charge model quickly and efficiently generates high-quality atomic charges for organic molecules suitable for computer simulations in the solution phase. The concept of the AM1-BCC charge model is to produce atomic charges that emulate the HF/6-31G* electrostatic potential (ESP). Underlying electronic structure features including formal charge and electron density delocalization are first captured by AM1 atomic charges; bond charge corrections (BCCs) are then simply added to these AM1 atomic charges to produce the AM1-BCC charges. The BCCs have been determined such that, when added to the AM1 atomic charges, the resulting AM1-BCC atomic charges emulate the HF/6-31G* ESP. The BCCs were parameterized against a training set of >2700 molecules sampling most organic functional groups and their combinations, as well as an extensive variety of cyclic and fused bicyclic heteroaryl systems. The resulting BCC parameters allow the AM1-BCC charging scheme to handle virtually all organic compounds in The Merck Index and the NCI Database. The AM1-BCC charge model reproduces ab initio dimer energies of a diverse set of molecules with an average error of 0.9 kcal/mol and experimental relative free energies of solvation of a diverse set of compounds with an average error 0.7 kcal/mol.