Basic ideas for the correction of semiempirical methods describing H-bonded systems

In this Letter, we show how semiempirical methods may be improved to describe hydrogen-bonded systems and proton transfer reactions. The approach consists in a redefinition of the core-core interaction terms that, as previously shown, are at the origin of spurious artifacts in standard methods. The parameterization of the new core-core functions is done using ab initio data of the intermolecular potential energy surfaces (PESs), which permits reaching the correct behavior at short and long interatomic distances. Here we report the parameters for O-O, O-H and H-H interactions. Extension to other atom pairs seems feasible, so the development of a semiempirical method adapted to the study of intermolecular interactions might be envisaged. (C) 2000 Elsevier Science B.V. All rights reserved.