STRUCTURAL AND ELECTRONIC-PROPERTIES OF SMALL CU-N CLUSTERS USING GENERALIZED-GRADIENT APPROXIMATIONS WITHIN 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 the local density approxim ation (LDA) and the generalized-gradient approximation (GGA) of Perdew and Wang for exchange and correlation. Three different levels of impr ovement upon the LDA are considered. In the first level, the GGA corre ction to the exchange-correlation energy is evaluated using the electr onic density and the atomic coordinates obtained in the LDA calculatio n. In the second level, the electronic density is obtained self-consis tently within the GGA while keeping the LDA structural configurations. In the third level, both electronic density and ionic positions are o btained fully self-consistently within the GGA. We found that the firs t level of approximation is already sufficient to correct the overbind ing found in the LDA. With respect to the LDA, the self-consistent GGA enhances the electron charge accumulation around the nuclei by deplet ing the interatomic bonding regions, (C) 1998 American Institute of Ph ysics. [S0021-9606(98)30240-8].