Anharmonicity hybrid models

In order to treat larger systems and/or high numbers of conformers or iso-topomers at the anharmonic level at a reasonable computational cost, it is possible to restrict the VPT2 treatment to a small part of the system on the basis of the spectroscopic observables of interest (for instance, the most intense bands of an IR of the Raman spectrum), by reducing the number of the normal modes treated at the anharmonic level. Such an approach, referred to as the reduced dimensionality VPT2 RD-VPT2) [55, 75] can be also combined with the hybrid model described in Section 10.3.2.5, allowing the treatment of complex macromolecular systems. 

Table 7.2 MUEs of Anharmonic Vibrational Frequencies (cm Computed by Several DFT/N07D and Hybrid CCSD(T) + DFT Models for HjCN, FCS, and NH2 Radicals as Compared to Experimental Data"...

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