Efficient dipole iteration in polarizable charged systems using the cell multipole method and application to polarizable water Original Research Article

The fast multipole method (FMM) and its Cartesian version, the cell multipole method (CMM), allow efficient computation of Coulomb energy and forces in molecular dynamics (MD) simulations. In another work [R. Kutteh and J.B. Nicholas, Implementing the cell multipole method for dipolar and charged dipolar systems, Comput. Phys. Commun., this issue], we implemented CMM for efficient and accurate computation of the energy and forces in dipolar and charged dipolar systems. While CMM provides an efficient way of computing energy and forces in large polarizable systems, the self-consistent dipole iteration remains a computational bottleneck in simulations of these systems. In this paper, we apply CMM (single-level) to substantially reduce the single-iteration time. We further reduce the single-iteration time using a refined CMM iterative algorithm. In addition, we introduce an iterative predictor scheme to reduce the number of iterations to self-consistency. We apply these algorithms to polarizable water using the polarizable SPC (PSPC) model. The “refined CMM/predictor” iterative algorithm is shown to be accurate and extremely efficient. It removes the dipole iteration computational bottleneck in simulations of large polarizable systems.