On the electronic and geometric structures of armchair GeC nanotubes: a hybrid densityfunctional study

Abstract

Ab initio calculations within the framework of hybrid density functional theoryand the finite cluster approximation have been performed for the electronic andgeometric structures of three different types of armchair germanium carbide nanotube,from (3, 3) to (11, 11). Full geometry and spin optimizations with unrestrictedsymmetry have been performed. Physically pertinent quantities of interest suchas the cohesive energies, band gaps, radial buckling, density of states, dipolemoments, and Mulliken charge distributions have been investigated in detail forall nanotubes. For type I nanotubes, the largest cohesive energy obtained is4.092 eV/atom, whereas for type II and type III nanotubes, the values are3.987 eV/atom and 3.968 eV/atom, respectively. For optimized type I nanotubes, Ge atoms moved toward the tube axis andC atoms moved in the opposite direction after relaxation, opposite to the trends observedin types II and III. The band gaps for type I nanotubes are larger than the bulk 3C-GeCgap, varying between 2.666 and 3.016 eV, while type II and type III nanotubes havesignificantly lower band gaps, with all nanotubes being semiconducting in nature. Mullikencharge analysis indicates primarily ionic behavior for type I GeC nanotubes and amixed ionic with covalent behavior for the other two types. None of the tubesappear to be magnetic. Applications in the field of nano-optoelectronic devices,molecular electronics, and band gap engineering are envisioned for GeC nanotubes.