Abstract
Ground and excited electronic states of the neutral, cationic, and anionic silicon pentamer and hexamer (Si5 and Si6) are investigated. Different geometries such as trigonal bipyramid (TBP; D3h), distorted-TBP (C2v), and edge-capped tetrahedron (ECT; C2v) for Si5 and tetragonal bipyramid (TEBP; D4h, D2h), edge-capped trigonal bipyramid (ECTBP; C2v) for Si6 were studied. We have employed a number of techniques such as large scale complete active-space multiconfiguration self-consistent field (CAS-MCSCF), mutireference singles+doubles configuration interaction (MRSDCI) computations up to 12 million configurations, Møller–Plesset (MP2) and coupled cluster singles and doubles+triple excitation estimate [CCSD(T)] techniques to investigate the low-lying electronic states, their geometries and energy separations of neutral, cationic and anionic Si5 and Si6. A A1g1 TEBP structure (D4h symmetry) is computed as the ground state for Si6, in accord with the previously suggested experimental assignments, while the Si5 cluster is found to have a TBP (D3h) ground state. The excitation energy, atomization energies, ionization potentials, and vertical and adiabatic electron affinities are computed and compared with the experimental results. Our computations of the excited states of these species have facilitated assignment of the anion X, A, and B bands of the photoelectron spectra of Si5− and Si6− observed by Neumark and co-workers.
Published Version
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