A systematic benchmarking of computational vibrational spectroscopy with DFTB3: Normal mode analysis and fast Fourier...

Computational vibrational spectroscopy serves as an important tool in the interpretation of experimental infrared (IR) spectra. In this article, we present a systematic benchmarking study of DFTB3 with two different computational vibrational spectroscopic methods, based on either normal mode analysis (NMA) or fast Fourier transform dipole autocorrelation function (FT-DAC). The results were compared with experimental data and theoretical calculations with B3LYP/cc-pVTZ. The empirical scaling factors for DFTB3/NMA, DFTB3-freq/NMA, and DFTB3/FT-DAC methods are 0.9993, 1.0059, and 0.9982, respectively. We also demonstrate the significance of anharmonicity and conformational sampling in vibrational spectroscopic calculations on flexible molecules. As expected, DFTB3/FT-DAC predicted the anharmonic vibrational peaks more accurately than DFTB3/NMA and NMA spectra are highly dependent on the initial structures. The potential limitations of DFTB3 for vibrational spectroscopic calculations and the challenges in assigning the FT-DAC spectral peaks were noted. DFTB3/FT-DAC is expected to serve as a promising technique in computational spectroscopy in complex biomolecular systems. © 2018 Wiley Periodicals, Inc.