Plain Ewald and PME

where ∑ ~n is the sum over all lattice vectors ~n = (Lxnx, Lyny, Lznz), nx,y,z ∈ N and Lx,y,z are the dimensions of the unit MD cell and ~xij = ~xj − ~xi. The “daggered” (†) summation indicates the exclusion of all pairs i = j inside the original unit MD cell (~n = ~0). Most molecular force fields provide exclusion schemes to exclude additional pairs, e.g., the so-called 1-3 exclusion excludes directly connected pairs and pairs with a direct common neighbor. Furthermore, some exclusion schemes may also modify the potential by a factor for certain pairs. If the potential φ satisfies |φ(~x)| ≤ A|~x|−3− (2)