The silicon hydride clusters Si3Hn (n ≤ 8) and their anions:: Structures, thermochemistry, and electron affinities

The molecular structures, electron affinities, and dissociation energies of the Si3Hn/Si3Hn- (n less than or equal to 8) species have been examined using five hybrid and pure density functional theory (DFT) methods. The basis set used in this work is of double-zeta plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated (Chem. Rev. 2002, 102, 231). 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 D-e (Si3Hn-->Si3Hn-1+H) for the neutral Si3Hn and D-e (Si3Hn--->Si3Hn-1-+H) for the anionic Si3Hn- species have also been reported. In the prediction of bond lengths, the BHLYP predicts the most reliable Si-Si bond lengths and the B3LYP predicts the most reliable Si-H bond lengths. The most reliable EA(ad), obtained at the B3LYP and BPW91 levels of theory, are 2.34 or 2.32 eV (Si-3), 2.56 eV (Si3H), 1.73 or 1.74 eV (Si3H2), 2.46 or 2.45 eV (Si3H3), 1.95 or 1.93 eV (Si3H4), 2.24 or 2.23 eV (Si3H5), 1.41 or 1.30 eV (Si3H6), and 2.14 eV (Si3H7). For Si3H8, there are no reliable EA(ad) but there are reliable VDE. The values of VDE for Si3H8 are 1.03 eV (B3LYP) or 1.10 eV (BPW91). The first dissociation energies (Si3Hn-->Si3Hn-1+H) predicted by all of these methods are 2.65similar to2.74 eV (Si3H), 2.82similar to3.12 eV (Si3H2), 2.13similar to2.23 eV (Si3H3), 2.92similar to3.08 eV (Si3H4), 2.63similar to2.95 eV (Si3H5), 3.29similar to3.53 eV (Si3H6), 2.19similar to2.54 eV (Si3H7), and 3.45similar to3.62 eV (Si3H8). For anion clusters (Si3Hn- --> Si3Hn-1-+H), the dissociation energies predicted are 2.89similar to2.95 eV (Si3H-), 2.01similar to2.27 eV (Si3H2-), 2.83similar to2.96 eV (Si3H3-), 2.37similar to2.68 eV (Si3H4-), 2.96similar to3.10 eV (Si3H5-), 2.36similar to2.74 eV (Si3H6-), 3.03similar to3.16 eV (Si3H7-), and 1.44similar to1.54 eV (Si3H8-).