The first HyDRA challenge for computational vibrational spectroscopy.

Vibrational spectroscopy in supersonic jet expansions is a powerful tool to assess molecular aggregates in close to ideal conditions for the benchmarking of quantum chemical approaches. The low temperatures achieved as well as the absence of environment effects allow for a direct comparison between computed and experimental spectra. This provides potential benchmarking data which can be revisited to hone different computational techniques, and it allows for the critical analysis of procedures under the setting of a blind challenge. In the latter case, the final result is unknown to modellers, providing an unbiased testing opportunity for quantum chemical models. In this work, we present the spectroscopic and computational results for the first HyDRA blind challenge. The latter deals with the prediction of water donor stretching vibrations in monohydrates of organic molecules. This edition features a test set of 10 systems. Experimental water donor OH vibrational wavenumbers for the vacuum-isolated monohydrates of formaldehyde, tetrahydrofuran, pyridine, tetrahydrothiophene, trifluoroethanol, methyl lactate, dimethylimidazolidinone, cyclooctanone, trifluoroacetophenone and 1-phenylcyclohexane-cis-1,2-diol are provided. The results of the challenge show promising predictive properties in both purely quantum mechanical approaches as well as regression and other machine learning strategies.

Improved modeling of anharmonicity for furan microsolvation.

Computational benchmark data for complexes requires accurate models of anharmonic torsional motion. State-of-the-art hindered rotor treatments come with a number of difficulties, regarding discontinuities from badly converged points or coupling, oscillations, or the consideration and correction of stationary points. Their manual handling introduces a level of arbitrariness not suitable for benchmark procedures. This study presents the TAMkinTools extension for improved modeling of one-dimensional hindered rotation which enables a more standardized workflow. We choose the structures from the Goebench challenge as test case, which comprises OH- and π-bonded complexes of methanol and furan, 2-methylfuran, and 2,5-dimethylfuran. Ahlrichs and Dunning basis sets of various sizes and their extrapolations show large differences in efficiency and accuracy for coupled-cluster energies of stationary points of these complexes. The probability density analysis of TAMkinTools provides zero-point energies for all conformations even within the same rotor profile. Zero-point energies show a large effect on the conformational order, especially for the methanol-furan complex with energy differences far below 1 kJ mol-1.