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.

本研究将 USPEX 进化搜索方法与采用色散校正的密度泛函理论（DFT-ulg）相结合，以预测高压下（100至500 GPa）NNO扩展固体的晶体结构。研究发现，在180 GPa以上，NNO纳米管（直径约为2.5 Å）是最稳定的形态。本文报告了该新型纳米管的结构稳定性、电子性质以及力学性质，并证实其在20 GPa以上保持稳定。为寻找在常压条件下可能稳定存在的类似结构，我们考虑了NPO管，并证实其在零压力下稳定。NPO相在25 GPa时导致绝缘体到金属的相变，此时PP范德华距离接近共价键距离。该NPO纳米管晶体的能量含量为10.6 kJ/g，比TNT高152%，比HMX高能材料高86%。这是结构能材料的第一例，可能具有重要应用价值，如点火器、燃烧弹、烟雾弹筛选装置等。此过程展示了在极端条件下进行材料发现，如何用于发现并稳定新型结构。