Similarities and differences in the Hartree-Fock and density-functional description of the chemisorption bond

The similarities and differences between the ab initio Hartree-Fock (HF) and density-functional theory (DFT) descriptions of the chemisorption bond have been explored by applying the constrained space orbital variation (CSOV) method to obtain and analyze the HF and DFT total energies of cluster models representing the interaction of CO and NH3 on Cu(100) and Pt(lll). 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 remains unchanged. The main quantitative effect of electronic correlation is to increase the inter-unit charge transfer but substrate polarization is also affected. A very important consequence emerges: it is not necessary to revise the physical mechanisms that have been previously proposed from the ab initio Hartree-Fock cluster model approach. (C) 1999 Elsevier Science B.V. All rights reserved.