DFT and AIMD analyses of the stability, electronic, optical, and thermal properties of BN polymorphs employing GGA and HSE06 functionals

Abstract This work examines the electronic structure, stability, thermal and optical properties of cubic boron nitride (c-BN) and orthorhombic boron nitride (o-BN) within distinct space groups. The electronic and structural properties of c-BN and o-BN are analyzed using GGA and HSE06 functional, revealing different characteristics influenced by their symmetry reflected by the space groups. c-BN exhibits a smaller direct band gap of 5.85 eV, whereas o-BN has a larger indirect band gap of 6.67 eV when calculated using HSE06. We explore the stability of c-BN and o-BN by evaluating their formation energy, phonon band structure, and their endurance during AIMD simulations. Both structures are energetically stable, with c-BN showing slightly higher stability. Phonon dispersion calculations confirm their dynamic stability. AIMD simulations highlight their excellent thermal stability, with o-BN proving more stable than c-BN under varying temperatures, as is evidenced by stable energy and temperature fluctuations throughout the simulations. The thermal properties of c-BN and o-BN structures are investigated focusing on heat capacity and lattice thermal conductivity. o-BN can hold more heat because it has a more complex phonon band structure, while c-BN conducts heat better because it has fewer phonon-phonon interactions and faster group velocity. These distinctions highlight their respective strengths for thermal management applications. The optical features of c-BN and o-BN are studied through their dielectric functions, showing that they absorb a lot of UV light due to transitions between energy bands. Both structures showed strong plasmonic activity and high UV refractive indices, highlighting their usefulness for applications in light control and photonics.