A FIRST PRINCIPLES STUDY OF SMALL CU-N CLUSTERS BASED ON LOCAL-DENSITY AND GENERALIZED-GRADIENT APPROXIMATIONS TO DENSITY-FUNCTIONAL THEORY

Neutral and anionic Cu-n clusters (Cu-2, Cu-3, Cu-6 and Cu-7(-)) are s tudied within density functional theory via (a) the local-density appr oximation (LDA) and (b) the generalized-gradient approximation (GGA) o f Perdew and Wang (GGA-PW) for exchange and correlation. GGA reduces b y similar to 20% the binding energies, while the bond lengths are incr eased by similar to 3-4%. The different levels of GGA approximation, i nvolving optimization of the electronic density and/or of the geometry , are shown in detail. In the case of Cu-6 the GGA configurational gro und state is a planar structure of D-3h symmetry. This result differs from the one obtained by LDA, where the three different isomers (one t wo-dimensional and two three-dimensional) were found to lie within 0.0 4 eV. Copyright (C) 1998 Elsevier Science B.V.