Edge Terminations Induced Structural Instability in 2D LP-N and HLP-N.

LP-N and HLP-N are promising high-energy-density materials. However, high-pressure synthesized samples cannot be quenched to 0 GPa. Furthermore, studies of their stability under ambient pressure are limited, and the underlying mechanism of their instability remains unclear. Based on first-principles and molecular dynamics methods, we systematically investigated their stability in both ideal crystal structures and edge-terminated configurations. Our results show that while ideal crystal structures of LP-N and HLP-N exhibit substantial static, dynamic, and mechanical stability at ambient pressure, the presence of edges leads to instability at the same pressure. LP-N shows modest stability improvement from H-saturated adsorption due to edge-initiated dissociation. Conversely, HLP-N relies on an interlocking mechanism for stability, which fails in the presence of edges, causing an internal breakdown. As a result, H-saturated adsorption has no stabilizing effect. The interlocking mechanism in HLP-N offers valuable insights into the design of new materials.