CSOV method

The nature of bonding of the adsorbed species to the model cluster of metal surfaces can be analyzed in terms of the so-called constrained space orbital variation (CSOV) method. For halogen anions adsorbed on various silver surfaces, it has been found that Pauli repulsion, metal polarization, and charge transfer to the metal surface mainly contribute to the binding energy of the ions [104, 301]. 

The different contributions to the HF, BLYP and B3LYP interaction energy of CO on the Pt 3(7,3,3) cluster model representation of the Pt(lll) surface as obtained at the various steps of the CSOV method are reported on Figure 2. The most important result of this comparison is that the qualitative picture of the chemisorption bond arising from ab initio HF and DFT quantum chemical approaches is essentially the same the relative importance of the different mechanisms remaining unchanged. This is an important conclusion because it validates many previous analysis of the chemisorption bond carried out in the framework of Hartree-Fock cluster model wave functions. " ... 

Figure 2. The interaction energy, E , in eV, of CO on Pti3(7,3,3) at the various steps of the CSOV method at HF and DFT levels of theory.

In our initial implementations of GEM-0 and GEM we have not introduced an explicit term for the dispersion interactions. This is because these force fields have been originally parametrized using the CSOV method at the DFT level, which, by definition, does not include a dispersion contribution. However, it is possible to include this term in a similar way to the SIBFA potential (Gresh et al., 1979 Piquemal et al., 2007). 

Its usefulness in the analysis of bonding in EDA complexes and hydrogen-bonded species notwithstanding, the above scheme has come under criticism on the grounds of its reliance on fictitious wavefunctions that violate the Pauli exclusion principle. Numerous formalisms that do not suffer from this serious conceptual flaw have been put forward. " Neither those foimalisms nor the constrained space orbital variation (CSOV) method, which has been employed in a... 

A particularly useful approach which provides unique information about the importance of different contributions to chemical bonding can be obtained with the constrained space orbital variation (CSOV) method. In this method, constraints are applied to the orbitals that are optimized in the variational procedure and in the space in which the restricted optimization is performed. The restrictions that are applied are based on chemical principles which allow certain types of interactions to occur and prevent others from occurring. The general... 

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