HIGH-LEVEL AB-INITIO VERSUS DFT CALCULATIONS ON (H2O2)(2) AND H2O2-H2O COMPLEXES AS PROTOTYPES OF MULTIPLE HYDROGEN-BOND SYSTEMS

The performance of B-LYP, B-P86, B3-LYP, B3-P86, and B3-PW91 density f unctionals to describe multiple hydrogen bond systems was studied. For this purpose we have chosen the dimers of hydrogen peroxide and the h ydrogen peroxide-water complexes. The geometries and vibrational frequ encies obtained with a 6-311 + G(d, p) basis set were compared with th ose obtained at the MP2 level using the same basis set expansion. The corresponding dimerization energies were obtained using a 6-311 + G(3d f, 2p) basis set and compared with those obtained using the G2(MP2) th eory. Red shiftings of the OH donor stretching frequencies were predic ted by all approaches investigated; however, in all cases, the DFT val ues were sizably larger than the MP2 ones. Similarly, the blue shiftin g of the torsion of the hydrogen peroxide subunit was larger when eval uated at the DFT level. AU functionals reproduced the G2(MP2) relative stabilities of the different local minima quite well. With the except ion of the B-LYP and B3-PW91 approaches, all functionals yielded bindi ng energies which deviated from the G2(MP2) values by less than 0.5 kc al/mol, provided that G2-type basis sets were used and that the corres ponding BSSE corrections were included. (C) 1997 by John Wiley & Sons, Inc.