A density functional theory study on parameters fitting of ultra long armchair (n, n) single walled boron nitride nanotubes

Armchair (n, n) single walled boron nitride nanotubes with n=2-17 are studied by the density functional theory at the B3LYP/3-21G(d) level combined with the periodic boundary conditions for simulating the ultra long model. The results show that the structure parameters and the formation energies bear a strong relationship to n. The fitted analytical equations are developed with correlation coefficients larger than 0.999. The energy gaps of (2, 2) and (3, 3) tubes are indirect gaps, and the larger tubes (n=4-17) have direct energy gaps. Results show that the armchair boron nitride nanotubes (n=2-17) are insulators with wide energy gaps of between 5.93 eV and 6.23 eV.