Local density functional study of copper clusters: A comparison between real clusters, model surface clusters, and the actual metal surface

Density Functional Theory is used to study the influence of the size of cop per clusters modeling the Cu(100) surface, on the electronic properties: io nization potential, electron affinity, electronic chemical potential, and c hemical hardness. The model clusters are chosen to have a bilayer structure and range in size from 9 to 20 copper atoms. The chemical hardness being i dentified as the relaxation energy of the frontier levels when an electron is removed or added to the system, a simple expression is proposed to estim ate its value from the eigenenergies of the frontier levels in neutral and partially ionized systems. A detailed comparison of the geometric and elect ronic structures is made between the model surface copper clusters, real co pper clusters, and the actual metal surface; it is seen that the model surf ace clusters provide an easy extrapolation to the properties of the metal s urface.