The possible structures of Pb~nS~n~-~1^+ (n=2～4) clusters have been studied by using density functional theory (B3LYP) method. It shows that the most stable isomers are Pb~S^+(C~2~v), Pb~3S~2^+(C~2~v) and Pb~4S~3^+(C~3~v), the most stable forms of the clusters. Meanwhile, the energies of the lowest unoccupied molecular orbitals (LUMO) are very low, this makes it easy for them to get an electron. It demonstrates that the corresponding neutral clusters exist stably.

Key words: AB INITIO CALCULATION, ELECTRONIC STRUCTURE, LEAD, SULFUR, GEOMETRICAL ISOMERISM