Next, we compare the the vibrational frequency predictions of DFTB and DFTB/ChIMES on 342 gas phase molecules from the Computational Chemistry Comparison and Benchmark Database or CCCBDB (). The reference data is at the MP2/cc-pVTZ level of theory. We also make comparisons with several DFT methods. The functionals chosen here are wB97XD, which is the same as wB97X with an additional dispersion correction, and the Perdew-Burke-Ernzerhof (PBE) functional. The predicted vibrational frequencies for those DFT functionals are also taken from CCCBDB. Figure shows the distribution of frequencies for each computational method. wB97XD gives good agreement with MP2 reference data with MAE/RMSE = 20/36 cm -1 . DFTB and PBE underestimate the vibrational stretching frequencies by about 100 cm -1 on average, where the MAE/RMSE are 77/114 and 61/79 cm -1 , respectively. DFTB/ChIMES yields smaller errors in the frequency prediction with MAE/RMSE = 36/61 cm -1 , showing notable improvement over PBE and comparable accuracy to wB97XD.