A method to integrate an atom in a molecule without explicit representation of the interatomic surface

A method to obtain accurate integrated properties according to the theory of "Atoms in Molecules" for any atom is proposed. Classical integration algorithms using explicit representations of the interatomic surfaces (IAS) bounding the integrated atom suffer from the presence of regions where the charge density is extremely flat. This phenomenon is typically caused by ring critical points and leads to unacceptable integration errors. The present paper extends a previously published integration algorithm (Mol. Phys. 87 (1996) 1169) by introducing a procedure that can find an atomic boundary if the interatomic surface is not explicitly known. This hybrid algorithm - which uses analytical interatomic surfaces whenever they are available and adequate but does not necessarily require them - enables the accurate and efficient integration of any atom. A robust and effective code is implemented in MORPHY97 and applied to two representative examples. © 1998 Elsevier Science B.V.