CellList

SimulationBuilder > Shared > Optimization

Cell lists are used to speed up soft matter simulations by reducing the number of times force or potential routines need to be called per time step. This optimization trick is based upon the fact that the interaction potential used to calculate the energy/forces between particles is typically "cut off" at a certain distance. That is, beyond a certain specified distance, particles cannot "feel" each other. The Lennard-Jones potential is usually taken to have a cutoff at r=2.5.

If the simulation box is sufficiently large (L>=3*cutoff), it can be split up into cells. Each cell? keeps track of the particles inside of it. When the force or potential routine is called during a simulation the cell list determines the order in which the particles are checked. First, a particle in the first cell computes its force/potential with other particles in the same cell and a carefully chosen subset of neighboring cells. This is repeated for the other particles in the first cell, and care is taken not to double-count any of the interactions. Once every particle in the first cell has been checked, the cell list chooses the next cell to be looped over, and this is repeated until every cell has been checked.