MODEL STUDIES OF THE CHEMISORPTION OF HYDROGEN AND OXYGEN ON NICKEL SURFACES .1. THE DESIGN OF A ONE-ELECTRON EFFECTIVE CORE POTENTIAL WHICH INCLUDES 3D RELAXATION EFFECTS

The present article is the first in a series describing investigations of the chemisorption and dissociation of hydrogen and oxygen on nickel surfaces. This paper deals with methodological questions, mainly concerning the form and properties of the crucial one-electron effective core potential (ECP) on nickel, which is used to describe chemisorption situations with sufficiently large nickel—adsorbate distances. Atomic chemisorption in the fourfold position on the Ni(100) surface is chosen as the model problem for testing and designing the nickel ECP. All-electron calculations on Ni4 and Ni5 with and without adsorbed atoms have been performed to produce reference results. Particularly noteworthy of the all-electron results is the large effect of 3d relaxation. To mimic cluster 3d relaxation effects a diffuse attractive 3d projection operator was added to the original standard form of the ECP