Predictions of novel polymorphs of boron nitride: a first-principles study

Physical properties of boron nitride (BN) have been studied in novel crystal structures such as hexagonal (h), wurtzite (w), 5-5, GeP, Li2O2, MoC, NiAs, and TiAs. The calculations of structural, electronic, and optical properties of BN have been carried out by "the full-potential linearized augmented plane wave plus local orbital (FP-LAPW + lo)" method framed within the "density functional theory (DFT)". The phonon band structures have been determined using the pseudo-potential-based approach realized in the CASTEP code, indicating that the h, w, 5-5, Li2O2, and MoC do not exhibit phonon modes at negative frequency, whereas, GeP, NiAs, and TiAs modifications exhibit phonon modes at the negative frequency. However, the novel polymorphs of BN demonstrated cohesive energies higher/comparable to that of the ground state h-BN. The lattice parameters of h and w structures of BN calculated through "Perdew-Burke-Ernzerhof-generalized gradient approximation (PBE-GGA)" are in good agreement with the available theoretical and experimental data. The band structures calculations indicate that BN crystallized in h, w, GeP, Li2O2, MoC, NiAs, and TiAs show indirect bandgap, whereas the 5-5 phase shows direct bandgap. The bandgap values show that h-BN and w-BN are insulators, and 5-5, GeP, Li2O2, MoC, NiAs, and TiAs are semiconductors. Optical parameters, such as the real part of the dielectric function, the imaginary part of the dielectric, reflectivity, absorption coefficients, and refraction spectrum related to all the considered polymorphs, have been studied. These novel polymorphs with greatly evolved physical behavior would be interesting for applications in the current semiconducting industry and other futuristic technologies.