DENSITY FUNCTIONAL THEORY STUDIES OF CHARGED, COPPER-DOPED, SMALL SILICON CLUSTERS, 
(n = 1–7)
Abstract
The structures and stabilities of charged, copper-doped, small silicon clusters 
(n = 1–7) have been systematically investigated using the density functional theory method at the B3LYP/6-311+G* level. For comparison, the geometries of neutral CuSin clusters were also optimized at the same level, although most of them have been reported previously [see Xiao CY, Abraham A, Quinn R, Hagelberg F, Comparative study on the interaction of scandium and copper atoms with small silicon clusters, J Phys Chem A106:11380, 2002; Liu X, Zhao GF, Guo LJ, Wang XW, Zhang J, Jing Q, Luo YH, First-principle studies of the geometries and electronic properties of CumSin (2 ≤ m + n ≤ 7) clusters, Chin Phys16:3359, 2007]. Our results for the ground state structures of neutral CuSin clusters agree well with those of Liu et al. and Xiao et al. except for CuSi3 and CuSi7. Removing or adding an electron greatly changes some ground state structures, i.e. for 
, 
, 
, 
, and 
; others are almost unchanged, e.g. 
, 
, 
, 
, 
. The ground states of ionic 
are all singlet, except for the smaller CuSi- and 
. Based on the optimized geometries, various energetic properties, including binding energies, second-order difference energies, the highest occupied molecular orbit and the lowest unoccupied molecular orbital (HOMO–LUMO) energy gaps, ionization potential and electron affinities, were calculated for the most stable isomers of 
. All the results indicate that anionic 
and cationic 
clusters are relatively stable. The higher stability of the latter has been confirmed by Beck's observations.
