A DENSITY-FUNCTIONAL STUDY OF WEAKLY-BOUND HYDROGEN-BONDED COMPLEXES

Density functional theory (DFT) calculations with B3LYP exchange-corre lation functional and using 6-31 + + G(d, p) basis functions have been performed on weakly bound hydrogen bonded complexes between HX (X = F , Cl) and alkenes and alkynes, such as C2H4, C2HX (X = H, F, Cl), C4H2 and allene. Calculations have also been carried out at MP2 = full lev el of theory and using the same basis set as mentioned above for compa rison with the DFT results. It has been observed that the BSSE uncorre cted binding energies obtained from the B3LYP calculations are always lower than the corresponding MP2 results whereas opposite trend has be en observed after BSSE correction. Hydrogen bond lengths obtained from MP2 and B3LYP calculations differ insignificantly. The H-X frequency shift due to complex formation has been well reproduced by the B3LYP m ethod. (C) 1998 Elsevier Science B.V. All rights reserved.