Abstract
A formalism has been developed to treat hydrogen‐bonded A—H…︁__B__ systems within the CNDO/2 and the MINDO/3 methodologies. In this formalism the interactions are divided into three distinct classes; those between (a) two hydrogen‐bonded atoms, (b) one hydrogen‐bonded and non‐hydrogen‐bonded atom, and (c) two non‐hydrogen‐bonded atoms. The last class of interactions is treated solely by the existing CNDO/2 or MINDO/3 method. For A –H…︁__B__ systems, the core resonance integrals are individually parametrized depending upon the class of the interaction. Three types of A—H…︁__B__ systems have been thus far parametrized. Nine hydrogen‐bonded dimers have been studied using the new formalism and the current CNDO/2 and the MINDO/3 methods. MINDO/3 predicts very large interatomic (A –B) distances for the equilibrium geometry, and relatively small stabilization values for the hydrogen‐bond energies. CNDO/2 predicts the reverse. The new formalism for both CNDO/2 and MINDO/3 predicts accurate geometries as well as energies for all nine dimers. The new formalisms are called CNDO/2H and MINDO/3H. A general discussion of the nature of hydrogen bonding as exhibited by CNDO/2H and MINDO/3H is presented.