Two simple approaches to quantifying this stacking would be by taking the energy contribution from dispersion, or the contact surface area, which are both easily extracted from standard output files. The contact surface area is the area of each molecule in the dimer in contact with the other monomer. A simple way to extract this value is to take the SASA (solvent accessible surface area) of the monomers and subtract the SASA of the dimer, then divide by two.