A Fast, Convenient, Polarizable Electrostatic Model for Molecular Dynamics

Abstract

We present an efficient polarizable electrostatic model, utilizing typed, atom-centered polarizabilities and the fast direct approximation, designed for efficient use in molecular dynamics (MD) simulations. The model provides two convenient approaches for assigning partial charges in the context of atomic polarizabilities. One is a generalization of RESP, called RESP-dPol, and the other, AM1-BCC-dPol, is an adaptation of the widely used AM1-BCC method. Both are designed to accurately replicate gasphase quantum mechanical electrostatic potentials. Benchmarks of this polarizable electrostatic model against gas-phase dipole moments, molecular polarizabilities, bulk liquid densities, and static dielectric constants of organic liquids show good agreement with the reference values. Of note, the model yields markedly more accurate dielectric constants of organic liquids, relative to a matched nonpolarizable force field. MD simulations with this method, which is currently parametrized for molecules containing elements C, N, O, and H, run only about 3.6-fold slower than fixed charge force fields, while simulations with the self-consistent mutual polarization average 4.5-fold slower. Our results suggest that RESP-dPol and AM1-BCC-dPol afford improved accuracy relative to fixed charge force fields and are good starting points for developing general, affordable, and transferable polarizable force fields. The software implementing these approaches has been designed to utilize the force field fitting frameworks developed and maintained by the Open Force Field Initiative, setting the stage for further exploration of this approach to polarizable force field development.

The Open Force Field Initiative: Open Software and Open Science for Molecular Modeling

“…LJ parameters to match it. In particular, AM1-BCC-dPol maintained the accuracy of densities of organic liquids and provided a marked improvement in the accuracy of their dielectric constants . Planned further studies of this approach include development of a water model and retraining of Lennard-Jones parameters within this paradigm, making it possible to provide quantitative evidence for what regimes might require treatment of polarizability for accuracy.…”

“…Wang and co-workers have now used OpenFF data sets and capabilities to prove the principle of a facile approach to including electronic polarizability in simulations, with the goal of gaining much of the potential increase in accuracy at a modest computational cost. 144 The method includes a set of typed polarizability parameters; i.e., atom-centered point polarizabilities that are assigned to a new molecule based on its 2D structure, rather than by using bespoke QM calculations. These polarizabilities were fitted to changes in the QM electrostatic potentials (ESPs) of a training set of molecules, and have been typed both by element and by LJ type.…”