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Keywords:

  • intermolecular interactions;
  • π–π charge-transfer spectra;
  • MO energies

Abstract

Various density functionals are applied to a number of weakly bound intermolecular π–π 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 Å too long. Various hybrid functionals with nonlocal exchange correction provide binding energies that compare favorably with the experimental heats of formation measured in solution. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 623–631, 2003