The geometric and electronic structure of small copper clusters Cunand Cu+n(n=1ndash;3) by an effective core potential method

摘要

Electronic structure calculations have been carried out for the total energy of the ground state of Cunand Cu+n(n=1ndash;3) clusters. The Cu atom is treated as a onehyphen;electron system and the effect of the core is approximated by a shape consistent pseudopotential and a semiempirical corehyphen;valence, corendash;core polarization potential. The exchange and correlation energies among the valence electrons are treated by the localhyphen;spinhyphen;densityhyphen;functional approximation with and without the selfhyphen;interaction corrections (SIC). The binding energy and bond distance of Cu2calculated with SIC are in almost exact agreement with experimental data. The calculated ionization potentials exhibit evenndash;odd oscillations as a function ofn. The potential energy surfaces of Cu3show substantial differences when obtained with and without SIC. The most stable geometry predicted by the latter is an acute triangle with an apex angle of 47deg; and a long bond length of 5.41 a.u. In terms of a distortion parameter rgr; with respect to an equilateral triangle with an equilibrium bond length of 4.78 a.u. we have rgr;=0.435 a.u. This is in excellent agreement with the experimental value of rgr;=0.472 a.u. The calculated binding energy of Cu3with respect to fragmentation into Cu atoms is 2.259 eV in comparison with the experimental value of 3.108plusmn;0.135 or 3.058plusmn;0.151 eV. The 27percnt; error is probably due to the use of local exchangehyphen;correlation energies and the somewhat small basis set.