Vibrational frequency prediction using density functional theory

A comparison of several density functional methods for calculating vibrational frequencies is reported. Methods examined include the local S-VWN (LSDA) functional, the non-local B-LYP and B-VWN functionals and the hybrid B3-LYP and B3-P86 functionals. The split-valence polarized 6-31G∗ basis set has been used in all methods. The computed frequencies were compared with experimental frequencies for a set of 122 molecules (a total of 1066 frequencies). All density functional theory (DFT) methods perform well for the calculation of vibrational frequencies, with overall root mean square errors (34–48 cm−1) significantly less than that reported for the MP2 theory (61 cm−1). The two hybrid functionals (B3-LYP and B3-P86) are more reliable than the S-VWN, B-LYP and B-VWN functionals. Scaling factors recommended for reproducing experimental fundamentals are 0.9833, 0.9940, 0.9820, 0.9613 and 0.9561, for S-VWN, B-LYP, B-VWN, B3-LYP and B3-P86, respectively. The performance of the various DFT methods on the calculation of zero-point energies is compared with experimental results for 24 molecules. Again, the hybrid functionals represent a significant improvement over the local and non-local density functionals.