High-pressure polymeric structures of nitrogen have attracted great attention owing to their potential application as high-energy-density materials. We report the density functional structural prediction of the unexpected stabilization of a diamondoid (or N10-cage) structure of polymeric nitrogen at high pressures. The structure adopts a highly symmetric body-centered cubic form with lattice sites occupied by N10 tetracyclic cages, each of which consists of 10 atoms and is covalently bonded with its six next-nearest N10 cages. The prediction of this diamondoid structure rules out the earlier proposed helical tunnel phase and demonstrates the high-order nature of polymeric nitrogen at extreme high pressures. Diamondoid nitrogen is a wide-gap insulator and energetically more favorable than the experimental cubic gauche and previously predicted layered Pba2 phases above 263 GPa, a pressure which is accessible to high pressure experiment.
@article{arxiv.1206.5668,
title = {Diamondoid Structure of Polymeric Nitrogen at High Pressures},
author = {Xiaoli Wang and Yanchao Wang and Maosheng Miao and Xin Zhong and Jian Lv and Jianfu Li and Li Chen and Chris J. Pickard and Yanming Ma},
journal= {arXiv preprint arXiv:1206.5668},
year = {2012}
}