I am currently using Qchem and as a beginner, I am uncertain which DFT-D has to be used with B3LYP functional within a system containing Donor and acceptor molecules bonded together by hydrogen bonding.
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It is probably best in that case to use
METHOD = B3LYP
EMPIRICAL_DISPERSION = TRUE
or else to use a functional such as wB97X-D that has the dispersion built in and doesn’t have to be turned on separately.