First-principles study of the structural, electronic, dielectric, and dynamical properties of gallium nitride in the graphite-like hexagonal P6₃/mmc phase

In this study, we investigate the structural, electronic, dielectric, and dynamical properties of gallium nitride in the hypothetical hexagonal P6₃/mmc phase through first-principles simulations. Electronic structure calculations show strong hybridization and a relatively small band gap of 1.34 eV. Dielectric property simulation demonstrates higher dielectric constants in the layer direction compared to the out-of-layer direction, attributed to the weaker van der Waals interactions between layers in the hexagonal structure. The Born effective charges suggest a predominantly ionic character in GaN, with significant anisotropy in charge distribution. Phonon band structure analysis reveals the presence of unstable phonon modes at the Γ and A points indicating dynamic instability in this configuration. Phonon band structure analysis reveals the presence of unstable phonon modes at the Γ and A points, indicating dynamic instability in this configuration. This instability can be controlled by applying external parameters, such as pressure, to synthesize GaN in this structure. Moreover, the detailed decomposition of the phonon modes provides insights into the structural instability, emphasizing the role of short-range interactions.