Ab initio study of structural and electronic properties of lithium fluoride nanotubes

Ionic compounds exhibit great structural diversity that can be used for tailoring novel nanostructured materials with distinct technological applications. In particular, significant progress has been made in the development of inorganic nanotubes, where the introduction of polar chemical bonds dramatically affects their physical properties in comparison to their carbon-based analogs. In this work, we apply density functional theory methods combined with plane-wave basis sets and periodic boundary conditions to investigate structural and electronic properties of prototypical lithium fluoride nanotubes featuring armchair, zig-zag, and square sheet (SSNT) configurations. Our results indicate that the zig-zag nanotubes can be formed from the more stable SSNT structures by the application of a positive axial strain, where an upper value of 1.44 eV for the activation energy is obtained. Furthermore, the zig-zag structures become more stable with the increasing nanotube radius, being merely 0.13 eV higher in energy than SSNT for the (10,0) case. All nanotubes investigated herein are insulators, with bandgap energies in the range of 8.33-8.59 eV for armchair and 7.91-8.54 eV for SSNT configurations. The latter nanotubes have higher Young's modulus, and consequently greater stiffness, than the corresponding armchair analogs. The small strain energies computed for the SSNT and armchair nanotubes reveal their high stability, making them promising candidates for experimental realization.