Boron Nanotube Structure Explored by Evolutionary Computations

In this work, we explore the structure of single-wall boron nanotubes with large diameters (about 21 Å) and a broad range of surface densities of atoms. The computations are done using an evolutionary approach combined with a nearest-neighbors model Hamiltonian. For the most stable nanotubes, the number of 5-coordinated boron atoms is about 63% of the total number of atoms forming the nanotubes, whereas about 11% are boron vacancies. For hole densities smaller than about 0.22, the boron nanotubes exhibit randomly distributed hexagonal holes and are more stable than a flat stripe structure and a quasi-flat B36 cluster. For larger hole densities (>0.22), the boron nanotubes resemble porous tubular structures with hole sizes that depend on the surface densities of boron atoms.