Energy Components in the Supermolecular Approach

In the supermolecular approach the interaction energy AE of a complex is obtained by evaluating the total energy E b of the AB supermolecule using method X (X = SCF, Cl, CEPA, MPn, CPF.) and subtracting the energy of the monomers  

The connection with the perturbation method may be made by assuming the exact eigenfunctions //q and ij/o to be available. Using ji/iI/qiPo as a zeroth-order dimer wavefunction the dimer energy is obtained as 

This quantity will be referred to as the dimer Heitler-London energy. Using [//, j/] = 0 and H = H° +V iX may be reduced to 

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