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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mn>20</mml:mn> <mml:mo> </mml:mo> <mml:msup><mml:mtext>cm</mml:mtext> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msup> </mml:mrow> <mml:annotation>$$ 20\ {\mathrm{cm}}^{-1} $$</mml:annotation></mml:semantics> </mml:math> 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.