Direct calculation of anharmonic vibrational states of polyatomic molecules using density functional theory: spectroscopic tests of recently developed functionals

The anharmonic vibrational frequencies of H2O, Cl-H2O and (H2O)(2) are calc ulated using potential energy surfaces computed from DFT, specifically the generalized-gradient approximation (GGA) functional HCTH and the hybrid fun ctional B97(2c). HCTH gives reasonable agreement with experiment and can be recommended in situations where the use of a hybrid functional would be di fficult. B97(2c) is found to be superior in accuracy to all other functiona ls tested and should be the functional of choice when the anharmonic potent ial energy surfaces of polyatomic systems are required for spectroscopic or similar applications. This point is illustrated by the excellent agreement with experiment obtained in calculations on formic and acetic acid using t he B97(2c) functional. (C) 2000 Elsevier Science B.V. All rights reserved.