Unveiling Bulk Modulus and Stretching Bond Force Constants of Cubic and Wurtzite Boron Nitride Structures: A DFT Study

The mechanical properties of cubic (c-BN) and wurtzite (w-BN) boron nitride structures were investigated and compared using density functional theory (DFT) with several exchange–correlation functionals. This research focuses on determining the bulk modulus (B) and, for the first time, the stretching bond force constants (kr), two fundamental parameters that describe the intrinsic stiffness and elastic resistance of these BN structures. Despite their structural similarity with the same tetrahedral coordination between atoms, c-BN and w-BN exhibit subtle differences in bond strength and compressibility that have not been fully clarified at the atomistic level. By systematically analyzing the influence of hybrid and semi-local functionals, consistent relationship between structural configuration and the predicted B and kr values of both c-BN and w-BN structures were established and compared. These findings not only validate DFT as a reliable approach for assessing the mechanical properties of BN polymorphs, but also offer key parameters for machine learning and advanced multiscale modeling. Therefore, this theoretical study contributes to understanding the origin of mechanical properties in BN structures and supports their design in applications where a particular hardness and stability are required.