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

Abstract

Electronic structure calculations have been carried out for the total energy of the ground state of Cun and Cu+n (n=1–3) clusters. The Cu atom is treated as a one-electron system and the effect of the core is approximated by a shape consistent pseudopotential and a semiempirical core-valence, core–core polarization potential. The exchange and correlation energies among the valence electrons are treated by the local-spin-density-functional approximation with and without the self-interaction corrections (SIC). The binding energy and bond distance of Cu2 calculated with SIC are in almost exact agreement with experimental data. The calculated ionization potentials exhibit even–odd oscillations as a function of n. The potential energy surfaces of Cu3 show 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 47° and a long bond length of 5.41 a.u. In terms of a distortion parameter ρ with respect to an equilateral triangle with an equilibrium bond length of 4.78 a.u. we have ρ=0.435 a.u. This is in excellent agreement with the experimental value of ρ=0.472 a.u. The calculated binding energy of Cu3 with respect to fragmentation into Cu atoms is 2.259 eV in comparison with the experimental value of 3.108±0.135 or 3.058±0.151 eV. The 27% error is probably due to the use of local exchange-correlation energies and the somewhat small basis set.