1. A parallel processing system for computing particle interactions, said parallel processing system comprising a plurality of computation nodes arranged according to a geometric partitioning of a simulation volume, wherein each computation node comprises storage for particle data, said particle data being associated with particles in a region of the geometrically partitioned simulation volume, and a communication system comprising links interconnecting the computation nodes, wherein each of the computation nodes comprises a processor subsystem, and wherein the processor subsystems of the computation nodes together coordinate computation of the particle interactions in a distributed manner.