The molecular structures, electron affinities, and dissociation energies of the Si5Hn/Si5Hn- (n = 3-12) species have been calculated by means of three density functional theory (DFT) methods. The basis set used in this work is of double-xi plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. The geometries are fully optimized with each DFT method independently. Three different types of the neutral-anion energy separations presented in this work are the adiabatic electron affinity (EA(ad)), the vertical electron affinity (EA(vert)), and the vertical detachment energy (VDE). The first Si-H dissociation energies for neutral Si5Hn and its anion have also been reported.