The interaction energies calculated, by DFT functionals, ranged from
−88.98 kcal/mol to −110.73 kcal/mol for 3FMH and −82.14 kcal/mol to
−104.41 kcal/mol for 3FLZ. These results are consistent with those of
MP2, indicating the importance of functional calculation with D3
dispersion correction. Among the DFT functionals, the results for higher
rungs of Jacob’s ladder showed lower interaction energies than those for
the lower rungs, such as TPSS versus B3LYP. The results using D3
correction showed improvements in describing weak interactions. MP2 is
more computationally expensive than DFT; however, the energy calculated
by MP2 was similar to that by DFT-D3 (such as M06-2x). Therefore, these
results suggested that DFT with dispersion correction is the better
choice for efficient calculation of interaction energy.