Quantum Chemical Studies on the Structural, Electronic, and Vibrational Properties of Boron Carbonitride Nanotubes

The structural, vibrational, and electronic properties of zigzag ( <b><i>n</i></b> , 0) BC₂N nanotubes are investigated in their most stable configuration, type IV. Studies are based on density functional theory (DFT) using the M06-2X/6-31G(d) level of theory. The property-structure relationship is investigated by focusing on the chirality index ( <b><i>n</i></b> ). Furthermore, to analyze the length dependence of the stability/reactivity of BC₂N nanotubes, short ( <b><i>n</i></b> = 5-14, <b><i>s</i></b> -BC _<b>2</b> NNTs) and long ( <b><i>n</i></b> = 5-13, <b><i>l</i></b> -BC _<b>2</b> NNTs) nanotubes were proposed, with average lengths of 18.07 and 26.74 Å, respectively. Total energy minimization, assuming nonmagnetic nature and charge neutrality, yielded the ground state of all nanostructures. Results show that the electrophilicity and nucleophilicity indices exhibit that the BC₂NNTs are electrophilic systems; however, an increase in the length of the nanotube triples its electrophilic character. The <b><i>s</i></b> -BC₂NNTs show a semiconductor character, while <b><i>l</i></b> -BC₂NNTs show a semiconductor-to-semimetallic character; therefore, the length of the nanotube is a key element for fine-tuning the conductive properties of these systems. Nanotubes of larger length and diameter are favored, based on analysis of cohesion energies. Furthermore, a longer axial length of the nanotube improves the solubility properties as it considerably increases the dipole moment and the solvation energy in water. Finally, BC₂NNTs showed polarization relative to the distribution of negative and positive charges, as indicated by molecular electrostatic potential maps. This is important for possible regioselective reactions. The set of BC₂NNTs studied in this work may be proposed for biological applications. Also, due to the molecular gap energy found in the range 0.35 < <i>E</i> _g < 1.6 eV, we propose that these structures could be applied in the fabrication of integrated circuits at the nanoscale.