An adaptive treecode for computing nonbonded potential energy in classicalmolecular systems

A treecode algorithm is presented for rapid computation of the nonbonded po tential energy in classical molecular systems. The algorithm treats a gener al form of pairwise particle interaction with the Coulomb and London disper sion potentials as special cases. The energy is computed as a sum of group- group interactions using a variant of Appel's recursive strategy. Several a daptive techniques are employed to reduce the execution time. These include an adaptive tree with nonuniform rectangular cells, variable order multipo le approximation, and a run-time choice between direct summation and multip ole approximation for each group-group interaction. The multipole approxima tion is derived by Taylor expansion in Cartesian coordinates, and the neces sary coefficients are computed using a recurrence relation. An error bound is derived and used to select the order of approximation Test results are p resented for a variety of systems. (C) 2000 John Wiley & Sons, Inc.