THEORETICAL-STUDY OF ELECTRONIC-STRUCTURES OF ONE-DIMENSIONAL MAGNETIC CLUSTERS COMPOSED OF DOUBLET LITHIUM AND COPPER ATOMS

The electronic structures of one-dimensional magnetic clusters compose d of doublet lithium and copper atoms were investigated by the unrestr icted Hartree-Fock (UHF), post UHF, their spin-projected wavefunctions , and DFT(B3LYP) in combination with the Heisenberg model. The calcula tion of the effective exchange integrals, J(ab) values, in the Heisenb erg model were first performed for the linear clusters composed of fro m 2 to 11 doubler lithium atoms at the UHF and UMP2 levels. The potent ial curves of the lowest (LS)- and highest (HS)-spin states of the clu sters were also depicted by these methods using total energies. Both m ethods showed that the electronic structures of the linear lithium clu sters are definitely divided into two regions at interatomic distances of 4.4 Angstrom. One is a magnetic region with antiferromagnetic spin -coupling between the magnetic sites (lithium atoms) in the regions la rger interatomic distances than 4.4 Angstrom. Another is an intermedia te region between chemical species with strong covalent bonding charac ter and magnetic species with strong correlation character in the regi ons of 3.0 Angstrom < R < 4.4 Angstrom. The approximate spin-projected UHF (APUHF) and UMP2 (APUMP2) did not alter the above-described behav ior. The spin projection effects on their shapes in the LS state becam e less important for the clusters with over 10 lithium atoms. Next, li near copper clusters composed of from 2 to 5 atoms were investigated a t the level of UMP2 and APUMP2, giving results indicating that the lin ear copper clusters are also divided into two characteristics similar to the linear lithium clusters. The DFT(B3LYP) method was also applied to both Li and Cu clusters, and the same conclusions were obtained as for the UHF and UMP2 methods. (C) 1998 Elsevier Science B.V. All righ ts reserved.