Consider a computational cell in three dimensions with edge length equal to the cut-off radius formula_1. The pairwise distance between all particles in the cell and in one of the neighbouring cells is computed. The cell has 26 neighbours: 6 sharing a common face, 12 sharing a common edge and 8 sharing a common corner. Of all the pairwise distances computed, only about 16% will actually be less than or equal to formula_1. In other words, 84% of all pairwise distance computations are spurious.