Density functional theory study of the hydrogen bonding interaction in formamide dimer

The hydrogen bonding of 1:1 complexes formed between formamide and formamide molecule has been completely investigated in the present study using density functional theory (DFT) method at varied basis set levels from 6-31G to 6-311++G(2d,2p). The large basis sets 6-311++G(d,p) and 6-311++G(2d,2p) have been employed to determine the equilibrium structure and vibrational frequencies of the interacting complexes. Five reasonable geometries on the potential energy hypersurface of formamide dimer system are considered with the global minimum, four of which are cyclic double-hydrogen bonded structure and one is one-hydrogen bonded structure. The optimized geometric parameters and interaction energies for various isomers at different levels are estimated. The infrared spectrum frequencies, IR intensities and the vibrational frequency shifts are reported. Finally the solvent effects on the geometries of the formamide dimer have also been investigated using self-consistent reaction-field (SCRF) calculations at the B3LYP/6-311++G** level. The results indicate that the polarity of the solvent has played an important role on the structures and relative stabilities of different isomers.