An alternative treatment, specific to isolated molecules, is the effective decoupling of the Coulomb interactions between the system and its unphysical periodic replicas. For this purpose, special Poisson solvers provide an expression of the potential induced by the cluster charge density when modeled in an infinitely replicated periodic setup. The method of Martyna and Tuckerman (MT) assumes that the density vanishes far enough from the boundaries of the box so that the potential can be seen as having the same periodicity as the simulation domain D. In this first/nearest image picture, the potential in the MT method converges towards the isolated system limit when the supercell is sufficiently expanded. Separating its action at short and long distance with the help of the parameter α (1/r = [erfc(αr) + erf(αr)]/r), the latter can be recast as