Comprehensive Assessment of GFN Tight-Binding and Composite Density Functional Theory Methods for Calculating Gas-Phase Infrared Spectra

Vibrational
spectroscopy is a valuable and widely used analytical tool for the
characterization of chemical substances. We investigate the performance
of semiempirical quantum mechanical GFN tight-binding and force-field
methods for the calculation of gas-phase infrared spectra in comparison
to experiment and low-cost (B3LYP-3c) density functional theory. A
data set of 7247 experimental references was used to evaluate method
performance based on automatic spectra comparison. Various quantitative
spectral similarity measures were employed for the comparison between
theory and experiment and for determining empirical scaling factors.
It is shown that the scaling of atomic masses provides an accurate
yet simple alternative to standard global frequency scaling in density
functional theory (DFT) and semiempirical calculations. Furthermore,
the method performance for 58 exemplary transition metal complexes
was investigated. The efficient DFT composite method B3LYP-3c, that
was introduced in the course of this work, was found to be excellently
suited for general IR spectra calculations. The GFN1- and GFN2-xTB
tight-binding methods clearly outperformed the PMx competitors. Conformational
changes were investigated for a subset of the data and are found to
have a mediocre strong influence on the simulated spectra suggesting
that the corresponding elaborate sampling steps may be neglected in
automated compound identification workflows.