Performance assessment of density-functional methods for tudy of charge-transfer complexes

Various density functionals are applied to a number of weakly bound intermolecular pi-pi charge-transfer (CT) complexes. Most functionals, including the recently developed mPWPW91 and mPW1PW91, grossly underestimate experimental excitation energies; good agreement is obtained only with the half-and-half hybrid BH&HLYP functional. PW91PW91 provides the best agreement with intermolecular distances measured in crystal, while the BH&HLYP values are about 0.1 Angstrom too long. Various hybrid functionals with nonlocal exchange correction provide binding energies that compare favorably with the experimental heats of formation measured in solution. (C) 2003 Wiley Periodicals, Inc.