Bonded ALMO-EDA functionals and references

Questions
#1

I’m looking at the examples for ALMO-EDA for bonded interactions (12.28 and 12.29) and have been wondering a few things:

  1. Both example molecules should have both exchange and correlation. Neither snippet uses the keyword METHOD, instead only use EXCHANGE. Why is that the case?
  2. Only one of the ALMO-EDA examples for non-bonded interactions specifies dispersion-free reference functionals. Should that be included in general for ALMO-EDA or not? If not, what are the criteria to judge whether to do so? And which energy contributions that are most heavily affected by their presence?
#2

Regarding (1), using EXCHANGE for composite functionals is older Q-Chem input notation but should be backwards compatible, e.g., METHOD = B3LYP should be equivalent to EXCHANGE = B3LYP (w/o specifying CORRELATION in the latter case). Or in the examples in question, EXCHANGE = wB97X-D is equivalent to METHOD = wB97x-D, while EXCHANGE = HF (w/o CORRELATION) is equivalent to Hartree-Fock. You should see the functional printed out just before the SCF iterations begin, so you can confirm.

I’ll leave (2) for someone else.

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#3

Thanks for the clarification!

#4

The dispersion-free functional is set to Hartree-Fock exchange by default (no correlation). This seems to work well for dispersion-corrected hybrid functionals such as wB97M-V, B3LYP-D3(BJ), etc. For dispersion-corrected semi-local functionals like B97M-V this can still be used, whereas another recommended option is the revPBE functional (DISP_FREE_X = revPBE, DISP_FREE_C = PBE).

The choice of this dispersion-free functional would only affect the partition between Pauli repulsion and dispersion as components of the frozen interaction energy.

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