The importance of many-body intermolecular interactions in molecular modeling has become better recognized. Polarization is perhaps the most important many-body interaction due to its slow spatial decay, and major efforts to incorporate classical models of polarization in empirical force fields are underway.   The improved accuracy in modeling phenomena such as solvation free energies, solute/solvent dynamics, and protonation states that could be afforded by explicit inclusion of polarization is fundamental and therefore has important implications for a range of problems in atmospheric chemistry, alternative energy research, and biology.  However, the computational cost of calculating polarization for each energy/gradient evaluation has limited its practical use. To reduce the computational cost of the full N-body polarization calculation, we truncate the N-body energy expansion at the level of 3-bodies. This reduces the computational cost in several ways. First, the calculation of the induced dipoles for groups of 1 body, 2 bodies, and 3 bodies may be calculated exactly with matrix inversion, obviating the expensive iterative calculation in full N-body polarization. Secondly, due to the fact that they are independent calculations under the 3-body approximation, the polarization energy for the system may be trivially parallelized. Finally, spatial cutoffs may be employed due to the rapid decay of the polarization energy with distance.  We first demonstrate that the 3-body approximation yields errors of 1-5% in the polarization energy for neutral systems compared to the N-body model.   We then report that judicious choice of a cutoff yields errors in polarization energy of 2-3%.  Our hybrid OpenMP/MPI parallel implementation scales reasonably in the strong scaling regime.  In the limit of large numbers of parallel tasks, O(N) scaling in the cost of the polarization energy and gradient is realized.  Finally, we report condensed-phase properties of water obtained with our polarization model.

3-Body approximation of polarization in the induced dipole model in the AMOEBA force field: Implementation and application to water

248th National Meeting (2014)

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