First-principles investigation of the electronic and optical properties of As2GeTe nanotubes

In this paper, the electronic and optical properties of the armchair and zigzag As2GeTe nanotubes are investigated. Calculations have been performed using QUANTUM-ESPRESSO computational package, which is based on the density functional theory and pseudopotential technique. The strain and formation energies computed for the equal diameter of the two armchair and zigzag systems are almost the same and converge to the reference As2GeTe monolayer by increasing the diameter of the nanotubes. For each diameter, the calculated strain energies are lower than the corresponding armchair and zigzag carbon nanotubes. The electronic calculations indicate that for both armchair and zigzag systems, As2GeTe nanotubes have a semiconductor characteristic with a direct band gap of approximately 1.0 eV within the generalized gradient approximation. Based on the phonon dispersion curve at ambient pressure, nanotube structures are dynamically stable. The optical band gap derived from the imaginary part of the dielectric function also verifies the electronic results. All types of nanotubes, except the armchair (4.4) nanotube, have an equal and very low optical reflectivity (similar to 0.05) in the far-ultraviolet frequencies, which is an interesting problem for the reflectivity application. Apart from the first diameter of the armchair structure, the values of Plasmon energies calculated for both armchair and zigzag As2GeTe nanotubes are almost identical. The nearly identical electronic and optical properties of different diameters of the As2GeTe nanotubes make them attractive from an application point of view.