Structure and properties of X2O and XYO (X, Y  Cl, Br) molecules: DFT vs. ‘classical’ ab initio calculations

Equilibrium structures, energies and vibrational frequencies of Cl2O, Br2O and ClOBr isomers have been calculated using five selected DFT techniques. Comparison with available experimental data shows that S-VWN (LSD Slater exchange and LSD Vosko, Wilk and Nusaieʹs correlation functional) and, to a lesser extent, B3-LYP (Beckeʹs three-parameter functional with the correlation functional of Lee, Yang and Parr) yield the most accurate results. These DFT techniques have been compared to recent CCSD(T) calculations by Lee, and, in the case of Cl2O isomers, to a variety of ‘classical’ ab initio methods. Regarding the equilibrium geometries and vibrational frequencies, they give results (especially in the hypervalent XYO series) comparable to CCSD(T). Regarding the energetic data, the DFT results exhibit important discrepancies and should be considered with some caution.