Hi !

I'm studying a Heme-Heme dimer (see sketch, chemdraw structure is one Heme ring) and I want to compare the energy of before and after complexation of the propionic acid side-chain to an Acetic acid molecule, I get a binding energy for the :

dimer + 2*AcOH --> dimer(AcOH)2

reaction of -46 000 kJ/mol.

when I do 2* AcOH --> (AcOH)2 I get around -80kJ/mol, which is what I expect.

I'm using the B97D/6-31G* functionnal/basis set for optimisation of the dimers and 631++G** for single point calculation.

Is this normal ? If not, what can I try ?

I definitely have a balanced equation, both in terms of number of atoms and number of electrons, and both dimer my optimisations converged to a minimum (no imaginary frequency).

Thanks for your help