A comprehensive study of the structural and electronic properties of the interesting onion-skin-like [As@Nil(12)AS(20)](3-) cluster ion, characterized by Moses et al. [Science 300 (2003) 778], was carried out using a plane-wave based density functional theory. The calculated interatomic distances agree well with experiment. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for [As@Ni(12)AS(20)](3-) are fivefold-degenerate with h(u) and h(g) symmetries, respectively, and its HOMO-LUMO gap is determined to be 0.2 eV lower than that Of C-60. The static dipole polarizability of [As@Nil(12)AS(20)](3-) is two times larger than that Of C-60. The optical gap of [As@Nil(12)AS(20)](3-) is redshifted by 1.4 eV relative to that Of C-60. The possibility of synthesis of [Sb@Pd12Sb20](3-) is proposed. (C) 2004 Elsevier B.V. All rights reserved.