Frequency Scale Factors for Some Double-Hybrid Density Functional Theory Procedures: Accurate Thermochemical Components for High-Level Composite Protocols

In the present study, we have obtained
geometries and frequency
scale factors for a number of double-hybrid density functional theory
(DH-DFT) procedures. We have evaluated their performance for obtaining
thermochemical quantities [zero-point vibrational energies (ZPVE)
and thermal corrections for 298 K enthalpies (ΔH298) and 298 K entropies (S298)] to be used within high-level composite protocols (using the W2X
procedure as a probe). We find that, in comparison with the previously
prescribed protocol for optimization and frequency calculations (B3-LYP/cc-pVTZ+d),
the use of contemporary DH-DFT methods such as DuT-D3 and DSD-type
procedures leads to a slight overall improved performance compared
with B3-LYP. A major strength of this approach, however, lies in the
better robustness of the DH-DFT methods in that the largest deviations
are notably smaller than those for B3-LYP. In general, the specific
choices of the DH-DFT procedure and the associated basis set do not
drastically change the performance. Nonetheless, we find that the
DSD-PBE-P86/aug′-cc-pVTZ+d combination has a very slight edge
over the others that we have examined, and we recommend its general
use for geometry optimization and vibrational frequency calculations,
in particular within high-level composite methods such as the higher-level
members of the WnX series of protocols. The scale
factors determined for DSD-PBE-P86/aug′-cc-pVTZ+d are 0.9830
(ZPVE), 0.9876 (ΔH298), and 0.9923
(S298).