where , and 2 represents is the total energy of FBNF , h-BN and 2 molecule respectively. The 2 and denotes the number of fluorine molecule and total number of atoms. Similarly, in cohesive energy expression, the is total energy of the preferred system having N atoms. represents the total energy of an isolated i (B,N,F) atom and is the number of a specific atom i per unit cell. The frozen phonon method implemented in the Vibra package of SIESTA is adopted for the phonon dispersion calculation. An accurate force matrix is achieved at 5 × 5 × 1 supercell of convergence. For optical properties calculations, a denser k-point mesh, i.e. 60 × 60 × 1, within the Monkhorst-Pack scheme and optical broadening of 0.1 eV is used. Optical calculations in SIESTA are based on the first order time dependent perturbation theory (TDP) . The complex dielectric function ( ( )) can be expressed as: