Structure evolution and electrical transport property of Si nanowire

•We model various optimized Si and its alloy nanowires.•We examine changes in the structure and physical properties of the nanowires with different radii.•The structure of the Si nanowires transforms as the radii of the carbon nanotubes increase.•The conductance of the alloy nanowires is even lower comparing with the pure Si nanowires.

Various optimized Si and its alloy nanowires, from a monoatomic chain to helical and multishell coaxial cylinder, have been obtained. Results reveal that the structure of the Si nanowires transforms as the radii of the carbon nanotubes increase, despite of the chirality of the CNTs. We also calculate the physical properties, such as density of states, transmission functions, current–voltage (I–V) characteristics, and conductance spectra (G–V) of optimized nanowires and alloy nanowires sandwiched between two gold contacts. Interestingly, compared with the pure Si nanowires, the conductance of the alloy nanowires is even lower.