Molecular orbital study of the interactions of CO molecules adsorbed on a W(111) surface

We present a molecular orbital calculation for interaction of CO on W(111) surface. The atomic superposition and electron delocalization molecular orbital (ASED-MO) method is employed to calculate geometries, binding energies and reduced overlap populations in order to understand alpha-state and beta-states behavior of the CO on W(111). A three-layer-thick (19, 12, 12) cluster with 43 tungsten atoms is used for modeling the W(111) surface. Geometry optimizations are performed for four end-on and five lying-down configurations. From the binding energies, it may be seen that the CO molecule in the lying-down configuration binding to the first layer was the most stable. The next configurations in order of decreasing stability are two others of lying-down binding with the first and the second layers and the end-on onefold configurations. From the electronic structures decomposed into the components of states (or bands), it is revealed that the main interactions in the lying-down configuration are di-sigma bonds originating from the 5 sigma orbital of CO and the sp-band of W. We propose the pseudo-di-sigma bonds bridged structure model to explain the stability of the lying-down configuration. Through this model, the binding energy and the dissociation of CO molecule on W(111) are discussed with available experimental works. (C) 1999 Elsevier Science B.V. All rights reserved.