EFFICIENT DIPOLE ITERATION IN POLARIZABLE CHARGED SYSTEMS USING THE CELL MULTIPOLE METHOD AND APPLICATION TO POLARIZABLE WATER

The fast multipole method (FMM) and its Cartesian version, the cell mu ltipole method (CMM),allow efficient computation of Coulomb energy and forces in molecular dynamics (MD) simulations. In another work [R. Ku tteh and J.B, Nicholas, Implementing the cell multipole method for dip olar and charged dipolar systems, Comput. Phys. Commun., this issue], we implemented CMM for efficient and accurate computation of the energ y and forces in dipolar and charged dipolar systems. While CMM provide s 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 C MM (single-level) to substantially reduce the single-iteration time. W e further reduce the single-iteration time using a refined CMM iterati ve 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) mode l. The ''refined CMM/predictor'' iterative algorithm is shown to be ac curate and extremely efficient. It removes the dipole iteration comput ational bottleneck in simulations of large polarizable systems.