Sincerely,
Saeed

As you know much better than me, a DFT-SAPT needs "grac_shift" values for monomers. Please consider the below template employed for a given DFT-SAPT calculation:

memory 55 gb

molecule {
0 1
F                  0.00000000    0.00000000   -1.85087700
H                  0.00000000    0.00000000   -0.86870700
--
-1 1
Cl                 0.00000000    0.00000000    1.03097600

units angstrom
no_reorient
symmetry c1
}

set {
    basis aug-cc-pVTZ
    df_basis_scf  aug-cc-pvtz-jkfit
    df_basis_sapt aug-cc-pvtz-ri
    scf_type DF
    guess sad
    freeze_core True
    sapt_dft_functional pbe0
    sapt_dft_grac_shift_a 0.157
    sapt_dft_grac_shift_b 0.215
}

energy('sapt(dft)')

The question is as follows:

the "sapt_dft_grac_shift_a" is always regarded to the monomer whose structure is given first (HF in the present case) and "sapt_dft_grac_shift_b" is always regarded to the monomer whose structure is given second (Cl anion in the present case). Is my statement quite correct?

If no, we should properly define monomer a (for which grac_shift_a is considered) and monomer b (for which grac_shift_b is considered). If possible, considering the given template, please let me know how these two monomers should explicitly and appropriately be defined in two blocks.

Sincerely,
Saeed