Energy and electronic characteristics of silicon polyprismanes: density functional theory study

We report structural, energetic and some electronic properties of [n, 4]-, [n, 5]-, and [n, 6] silaprismanes (polysilaprismanes), i. e. silicon nanotubes of a special type constructed from dehydrogenated molecules of cyclosilanes (silicon rings) Si-4(-), Si-5(-), and Si-6, respectively. For large n, polysilaprismanes can be considered as the analogs of silicon nanotubes with an extremely small cross-section in the form of a regular polygon. Binding energies, interatomic bonds, and the energy gaps between the highest and lowest occupied molecular orbitals (HOMO and LOMO, respectively) have been calculated using the density functional theory for the systems up to ten layers. It is found that [n, 4] silaprismane is not thermodynamically stable in the bulk limit (n ->infinity), while the [n, 5]-and [n, 6] silaprismanes conserve their highly strained framework and become more thermodynamically stable as the number of layers n increases. Moreover, the HOMO-LUMO gap analysis reveals that the [n, 5]-and [n, 6] silaprismanes with the large effective length can be referred to semimetals or even the conductors. So, they can be successfully used unlike the carbon analogs in nanoelectronics as functional nanowires or the basis for the computational logic elements without any additional doping or applying the mechanical stresses. Thicknesses of silaprismanes are comparable with that of the smallest carbon nanotubes.