The lowest energy configurations of silicon doped carbon clusters of intermediate size (CnSim, n+m=11,12, m=1,2,3) are investigated using generalized tight binding molecular dynamics scheme and ab initio calculations. Our results favor low dimensional structures over three-dimensional arrangements for these clusters. This trend is in agreement with photolysis experiments that suggest linear chains to be more stable isomers. (C) 2003 American Institute of Physics.