A comparative study of the interaction of M (M = Sc, Cu) atoms with small Si-n (n = 1-6) clusters is performed by means of a hybrid density functional technique (B3LYP) in conjunction with a 6-311+G(d) basis set. The structures identified for the most stable isomers of MSin are usually different for M = Se and Cu, showing different growth patterns of these two clusters. Charge transfer is found to proceed from M to the Si-n framework in all MSin clusters and is stronger for M = Sc than for M = Cu. A mixed ionic, and covalent bonding picture between M and Si atoms emerges for MSin. Strong hybridization exists between Sc d and Si orbitals in ScSin, while the d shell of Cu in CuSin, remains nearly closed and contributes little to the Cu-Si bonding. On the basis of the optimized geometries, various energetic properties are calculated for the most stable isomers of MSin, including the binding and fragmentation energies, vertical and adiabatic ionization potentials, and electron affinities. Both the binding and fragmentation energies indicate that MSi2 and MSi5 have enhanced stability and could be produced with high abundance in mass spectrum.