Total energy partitioning within a one-electron formalism: A Hamilton population study of surface-CO interaction in the c(2 x 2)-CO/Ni(100) chemisorption system

A scheme for total electronic energy partitioning within the framework of a one-electron theory of the extended Huckel-type is presented, with a view to extending and augmenting the capabilities of existing theoretical electr onic structure analysis tools, specifically overlap population analysis. A total electronic energy partitioning is developed first for molecular and s ubsequently extended materials. In constructing the partitioning, we define molecular orbital Hamilton populations (MOHP's) for discrete systems, and Crystal Orbital Hamilton Populations (COHP's) for extended systems. The var ious energy partitionings and overlap population analyses are exemplified a nd contrasted for HX (X=F,Cl,Br), ethane, and a [PtH4](2-) polymer. The uti lity of energy partitioning is demonstrated by effecting a COHP partitionin g of the surface-CO interaction for the c(2x2)-CO/Ni(100) chemisorption sys tem. Aspects of the surface-CO interaction less amenable to overlap populat ion analysis are addressed, specifically the role of energetically low-lyin g filled CO orbitals and the relative contributions of surface s, p, and d bands to surface-CO interaction. Hamilton population analysis leads to a CO (4 sigma, 5 sigma)-metal forward donation, metal-CO(2 pi*) backdonation mo del for the surface-CO interaction. The metal sigma contribution to surface -CO bonding is described as sp dominated metal spd hybrid-CO bonding, modif ying slightly the metal d-CO sigma bonding model proposed by Blyholder. The metal d-2 pi* backdonation of the Blyholder model remains. The role of the CO(1 pi) orbitals is also discussed in the context of CO orbital mixing on binding CO to the Ni(100) surface. (C) 1999 American Institute of Physics. [S0021-9606(99)30325-1].