Parametrizing a polarizable force field from ab initio data. I. The fluctuating point charge model

We have developed a polarizable force field for peptides, using all-atom OPLS (OPLS-AA) nonelectrostatic terms and electrostatics based on a fluctuating charge model and fit to ab initio calculations of polarization responses. We discuss the fitting procedure, and specific techniques we have developed that are necessary in order to obtain an accurate, stable model. Our model is comparable to the best existing molecular mechanics force fields in reproducing quantum-chemical peptide energetics. It also accurately reproduces many-body effects in many cases. We believe that straightforward extensions of our linear-response electrostatic model will significantly improve the accuracy for those cases that the present model does not adequately address.