DENSITY FUNCTIONAL THEORY STUDIES OF CHARGED, COPPER-DOPED, SMALL SILICON CLUSTERS, ${\rm CuSi}_{n}^{+}/{\rm CuSi}_{n}^{-}$ (n = 1–7)

Abstract

The structures and stabilities of charged, copper-doped, small silicon clusters [Formula: see text] (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 CuSi n 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 Cu m Si n (2 ≤ m + n ≤ 7) clusters, Chin Phys16:3359, 2007]. Our results for the ground state structures of neutral CuSi n 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 [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]; others are almost unchanged, e.g. [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]. The ground states of ionic [Formula: see text] are all singlet, except for the smaller CuSi- and [Formula: see text]. 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 [Formula: see text]. All the results indicate that anionic [Formula: see text] and cationic [Formula: see text] clusters are relatively stable. The higher stability of the latter has been confirmed by Beck's observations.