Computer programs SUPERMOLECULE program

The basis set used for calculations were the STO-3G, the 3-21G, and the 6-31G basis sets, as implemented by the Gaussian-88 computer program. The energies of interaction were computed by using the supermolecule approach where the sum of the energies of the subsystems are substracted from the energy of the complex. All the species were geometry optimized. 

Unfortunately, the supermolecule approach [81, M] is full of technical difficulties, which stem chiefly from the very small magnitude of the interaction energy relative to the energy of the supermolecule. Even today, a novice would be ill-advised to attempt such a computation using one of the black-box computer programs available for performing ab initio calculations. 

Most popular in the ab initio calculation of intermolecular potentials is the so-called supermolecule method, because it allows the use of standard computer programs for electronic structure calculations. This method automatically includes all the electrostatic, penetration and exchange effects. If the calculations are performed at the SCF (self-consistent field) level the induction effects are included, too, but the dispersion energy is not. The latter, which is an intermolecular electron correlation effect, can be obtained by configuration interaction (Cl), coupled cluster (CC) calculations or many-body perturbation theory (MBPT). These calculations are all plagued... 

For the computation of the interaction between two closed-shell monomers there are at present two excellent computational methods, both implemented in black box programs. The first is based on SAPT [135] and the second is the supermolecule CCSD method [136,137] with triply excited terms added in a non-iterative fashion. 

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