A density functional theory study of the dimers of HX (X = F, Cl, and Br)

The geometries, interaction energies, and vibrational properties of (HF)(2), (HCl)(2), and (HBr)(2) have been investigated using a variety of hybrid density functional methods and the 6-311+G(2df,p) basis set. Although most of the density functional methods predict geometries in reasonable agreement with experiment, methods containing the LYP correlation functional yield geometrical parameters in slightly better agreement. The (HF)(2) interaction energy, predicted by the hybrid density functional methods, is in reasonable agreement with experiment, but the (HCl)(2) and (HBr)(2) interaction energies are underestimated substantially, The frequency shift for the X-H donor bond correlates linearly with the elongation of the X-H bond upon complexation, and is predicted reasonably well by methods containing the LYP functional. Overall, the hybrid density functional methods adequately predict the properties of the halide dimers. It is interesting to note that the BHandHLYP and B1LYP density functional methods offer a competitive alternative to the popular B3LYP method. (C) 2001 John Wiley & Sons, Inc.