Ionization of medium-sized silicon clusters and the geometries of the cations

Abstract

Articles you may be interested inThe effect of ionization on the global minima of small and medium sized silicon and magnesium clusters Energies and spatial features for the rotationless bound states of He 3 + 4 ( Σ g + 2 ) : A cationic core from helium cluster ionization One-photon mass-analyzed threshold ionization spectroscopy of 1,3,5-trifluorobenzene: The Jahn-Teller effect and vibrational analysis for the molecular cation in the ground electronic state Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of hexafluorobenzene: The Jahn-Teller effect and vibrational analysis Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of p -, m -, and o -difluorobenzenes. Ionization energies and vibrational frequencies and structures of the cationsWe have performed a systematic ground state geometry search for the singly charged Si n cations in the medium-size range (nр20) using density functional theory in the local density approximation ͑LDA͒ and generalized gradient approximation ͑GGA͒. The structures resulting for nр18 generally follow the prolate ''stacked Si 9 tricapped trigonal prism'' pattern recently established for the lowest energy geometries of neutral silicon clusters in this size range. However, the global minima of Si n and Si n ϩ for nϭ6, 8, 11, 12, and 13 differ significantly in their details. For Si 19 and Si 20 neutrals and cations, GGA renders the prolate stacks practically isoenergetic with the near-spherical structures that are global minima in LDA. The mobilities in He gas evaluated for all lowest energy Si n ϩ geometries using the trajectory method agree with the experiment, except for nϭ18 where the second lowest isomer fits the measurements. The effect of gradient corrections for either the neutral or cationic clusters is subtle, but their inclusion proves to be critical for obtaining agreement with the mobility measurements in the nϭ15-20 range. We have also determined ionization potentials for our Si n neutral geometries and found that all experimental size-dependent trends are reproduced for nр19. This particularly supports our structural assignments for Si 9 , Si 11 , Si 12 , and Si 17 neutrals. The good overall agreement between the measured and calculated properties supports the elucidation of the ''prolate'' family of silicon clusters as stacks of trigonal prisms.

Thermodynamics of tin clusters

“…Density-functional theory (DFT) studies of ground-state structures 5,6,7,8,9,10,11 and optical response 12 confirmed the prolate shape of the small sizes and showed further that many of the ground-state structures in this size range contain the tricapped trigonal prism (TTP) unit, a nine-atom unit consisting of a triangular prism capped by one atom on each of the three side faces.…”

Global geometry optimization of silicon clusters described by three empirical potentials

“…A central issue concerning the small clusters Si n is their lowest-energy geometric structures, namely, their global minima as a function of the cluster size n. For nр7, the global minima are firmly established by both ab initio calculations and Raman or infrared spectroscopy measurements, whereas for nр13 the global minima are also well established by ab initio calculations. 10,28,29 For 14рnр20, the global minima have been predicted based on semiempirical tight-binding ͑TB͒ and density functional theory ͑DFT͒ calculations 23,24 coupled with the genetic algorithm ͑GA͒ global optimization technique. 30 For Si 20 , in particular, the global minimum has been confirmed by the quantum Monte Carlo calculation.…”

Stabilized silicene within bilayer graphene: A proposal based on molecular dynamics and density-functional tight-binding calculations

“…Thus, we found that the structure of Si clusters inside bilayer graphene is totally different from free standing Si clusters (see, e.g., Ref. 42 ) and for N >5 resembles (but are not identical) the ones observed for carbon clusters in vacuum 41 .…”