Accuracy and Scaling Factors of Non-Empirical Double-Hybrid Density Functionals for Harmonic and Fundamental Frequencies (And ZPVE).

We obtain here scaling factors for harmonic and fundamental vibrational frequencies, as well as for Zero-Point Vibrational Energies (ZPVE), using the HFREQ2014 dataset of reference values. We consider a set of (non-empirical) double-hybrid density functionals, also including spin-scaled and range-separated versions, namely PBE-QIDH, RSX-PBE-QIDH, SOS1-PBE-QIDH, and SOS1-RSX-PBE-QIDH. We also analyze the dependence of the results with respect to the size of def-nVP(PD) basis sets of increasing angular momentum, with the def2-TZVPD basis set providing the best trade-off between accuracy and computational cost for all the functionals considered. Actually, (SOS1-)PBE-QIDH double-hybrid functionals are able to provide average errors as low as 20   cm - 1 $$ 20\ {\mathrm{cm}}^{-1} $$ for both types of frequencies, and lower than 0.1 kcal/mol for ZPVE, considerably better than the corresponding range-separated (spin-scaled or not) versions (SOS1-)RSX-PBE-QIDH. Therefore, accurate thermochemical calculations or vibronically-resolved spectra will expectedly benefit from the scaling factors derived here and the assessment of double-hybrid density functionals done along this work.