The electrostatic potential generated by topological atoms: a continuous multipole method leading to larger convergence regions

The electrostatic potential generated by an atom in a molecule can be conveniently expressed by traditional multipole expansions. The disadvantage of such expansions is that they introduce a divergence sphere within which the expansion diverges. Because of their finite size, atoms defined according to quantum chemical topology (QCT) yield a small divergence sphere. However the introduction of an alternative continuous multipole expansion reduces the divergence region even further. The new method allows the electrostatic potential to be evaluated accurately at short-range, which is illustrated for a pair of simple molecules.