Long-range Lattice-Gas Algorithm

Presented is a novel algorithmic method for simulating complex fluids, for instance multiphase single component fluids and molecular systems. The algorithm falls under a class of single-instruction multiple-data computation known as lattice-gases, and therefore inherits exact computability on a discrete spacetime lattice. Our contribution is the use of nonlocal interactions that allow us to model a richer set of physical dynamics, such as crystallization processes, yet to do so in a way that remains locally computed. A simple computational scheme is employed that allows all the dynamics to be computed in parallel with two additional bits of local site data, for outgoing and incoming messengers, regardless of the number of long-range neighbors. The computational scheme is an efficient decomposition of a lattice-gas with many neighbors. It is conceptually similar to the idea of virtual intermediate particle momentum exchanges that is well known in particle physics. All 2-body interactions along a particular direction define a spatial partition that is updated in parallel. Random permutation through the partitions is sufficient to recover the necessary isotropy as long as enough momentum exchange directions are used. The algorithm is implemented on the CAM-8 prototype.