The small silicon clusters Sin (n=2-10) and their anions: structures, themochemistry, and electron affinities

The silicon clusters structures, electron affinities, and dissociation energies of the Sin/Sin− (n=2-10) species have been examined using seven hybrid and pure density functional theory (DFT) methods. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. The geometries are fully optimized with each DFT method independently. Four different types of energy separations presented in this work are the adiabatic electron affinity (EAad), zero-point vibrational energies (ZPVE) corrected EAad (EAzero), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The first Si-Si dissociation energies De (Sin→Sin−1+Si) for Sin, and both De(Sin−→Sin−1+Si−) and (Sin−→Sin−1−+Si) for Sin− species have also been reported. The most reliable adiabatic electron affinities, obtained at the DZP++ BPW91 level of theory, are 2.16 (2.15) eV for Si2, 2.32 (2.32) eV for Si3, 2.24 (2.25) eV for Si4, 2.51 (2.51) eV for Si5, 2.11 (2.12) eV for Si6, 2.06 (2.07) eV for Si7, 2.86 (2.85) eV for Si8, 2.28 (2.28) eV for Si9, 2.45 (2.46) eV for Si10. (EAzero values are in parentheses). While BP86, B3P86 and BPW91 predict to the most reliable dissociation energies. The dissociation energies for Sin→Sin−1+Si are predicted to be 3.26 (3.23) eV for Si2, 3.96 (3.92) eV for Si3, 4.39 (4.33) eV for Si4, 3.68 (3.62) eV for Si5, 4.12 (4.08) eV for Si6, 4.07 (4.01) eV for Si7, 2.76 (2.73) eV for Si8, 4.28 (4.22) eV for Si9, 4.33 (4.28) eV for Si10 with error of 0.13 (0.16) eV (corrected with ZPVE in parentheses). And the dissociation energies of Sin−→Sin−1−+Si are predicted to be 3.95 (3.92) eV for Si2−, 4.14 (4.11) eV for Si3−, 4.29 (4.24) eV for Si4−, 3.98 (3.92) eV for Si5−, 3.72 (3.68) eV for Si6−, 4.01 (3.96) eV for Si7−, 3.59 (3.54) eV for Si8−, 3.69 (3.63) eV for Si9−, and 4.51 (4.46) eV for Si10−.