A density functional study of weakly bound hydrogen bonded complexes Original Research Article

Density functional theory (DFT) calculations with B3LYP exchange-correlation 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 level of theory and using the same basis set as mentioned above for comparison with the DFT results. It has been observed that the BSSE uncorrected binding energies obtained from the B3LYP calculations are always lower than the corresponding MP2 results whereas opposite trend has been 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 method.