To simulate physical processes, state vectors for each of multiple voxels are stored in a memory along with a representation for each of multiple facets that are sized and oriented independently of the size and orientation of the voxels and, in combination, represent one or more surfaces. Each state vector includes multiple entries, each of which corresponds to a number of elements at a particular momentum state of multiple possible momentum states at a voxel. Interaction operations that model interactions between elements of different momentum states are performed on the state vectors, and surface interaction operations that model interactions between a facet and elements at one or more voxels near the facet are performed on the representations of facets. Finally, move operations that reflect movement of elements to new voxels are performed on the state vectors.