Route to Stabilize Cubic Gauche Polynitrogen to Ambient Conditions via Surface Saturation by Hydrogen

Cubic gauche polynitrogen (cg-N) is an attractive high-energy density material. However, high-pressure synthesized cg-N will decompose at low pressure and cannot exist under ambient conditions. Here, the stabilities of cg-N surfaces with and without saturations at different pressures and temperatures are systematically investigated based on first-principles calculations and molecular dynamics simulations. Pristine surfaces at 0 GPa are very brittle and will decompose at 300 K, especially (110) surface will collapse completely just after structural relaxation, whereas the decompositions of surfaces can be suppressed by applying pressure, indicating that surface instability causes the cg-N decomposition at low pressure. Due to the saturation of dangling bonds and transferring electrons to the surfaces, saturation with H can stabilize surfaces under ambient conditions, while it is impossible for OH saturation to occur solely from obtaining electrons from surfaces. This suggests that polynitrogen is more stable in an acidic environment or when the surface is saturated with less electronegative adsorbates.