Stability of NNO and NPO Nanotube Crystals

We combine the USPEX evolution searching
method with density functional
theory using dispersion corrections (DFT-ulg) to predict the crystal
structure of the NNO extended solid at high pressures (from 100 to
500 GPa). We find that the NNO nanotube (with diameter ≈ 2.5
Å) is the most stable form above 180 GPa. We report here the
stability, electronic properties, and mechanical properties of this
novel nanotube and show that it is stable above 20 GPa. To find a
similar structure that might be stable at ambient conditions, we considered
the NPO tube and show that it is stable at zero pressure. The NPO
phase leads to an insulator to metal transition at 25 GPa, where the
PP van der Waals distance approaches the covalent bond distance. The
energy content of this NPO nanotube crystal is 10.6 kJ/g, which is
152% higher than that of TNT and 86% higher than that of the HMX energetic
material. This is the first example of a structural energetic material,
which could have important applications in igniters, incendiaries,
screening smoke ammunition, and similar devices. This process illustrates
how materials discovery in extreme conditions can be used to discover
and stabilize novel structures.