Predicting the crystal structure of $$\hbox {N}_5\hbox {AsF}_6$$ high energy density material using ab initio evolutionary algorithms

Abstract$$\hbox {N}_5\hbox {AsF}_6$$ N 5 AsF 6 is the first successfully synthesized salt that has a polymeric nitrogen moeity ($$\hbox {N}_5^+$$ N 5 + ). Although 12 other $$\hbox {N}_5^+$$ N 5 + salts followed, with $$\hbox {N}_5\hbox {SbF}_6$$ N 5 SbF 6 and $$\hbox {N}_5\hbox {Sb}_2\hbox {F}_{11}$$ N 5 Sb 2 F 11 being the most stable, the crystal structure of $$\hbox {N}_5\hbox {AsF}_6$$ N 5 AsF 6 remains unknown. Currently, it is impossible to experimentally determine the structures of $$\hbox {N}_5\hbox {AsF}_6$$ N 5 AsF 6 due to its marginal stability and explosive nature. Here, following an ab initio evolutionary prediction and using only the stoichiometry of $$\hbox {N}_5\hbox {AsF}_6$$ N 5 AsF 6 as a starting point, we were able to reveal the crystal structure of this high energy density material (HEDM). The $$\hbox {C}_{2V}$$ C 2 V symmetry of the $$\hbox {N}_5^+$$ N 5 + cation, as suggested from earlier investigations, is confirmed to be the symmetry adopted by this polymeric nitrogen within the crystal. This result gave full confidence in the validity of this crystal prediction approach. While stability of the $$\hbox {N}_5^+$$ N 5 + within the crystal is found to be driven by electronic considerations, the marginal stability of this HEDM is found to be related to a partial softening of its phonon modes.

Predicting High Energy Density Materials using Abinitio Evolutionary Algorithms: The Results for N5AsF6

N5AsF6 is the first successfully synthesized salt that has a polymeric nitrogen moeity (N5+). Although 12 other N5+ salts followed, with N5SbF6 and N5Sb2F11 being the most stable, the crystal structure of N5AsF6 remains unknown. Currently, it is impossible to experimentally determine the structures of N5AsF6 due to its marginal stability and explosive nature. Here, following an ab initio evolutionary prediction and using only the stoichiometry of N5AsF6 as a starting point, we were able to reveal the crystal structure of this high energy density material (HEDM). The C2V symmetry of the N5+ cation, as suggested from earlier investigations, is confirmed to be the symmetry adopted by this polymeric nitrogen within the crystal. This result gave full confidence in the validity of this crystal prediction approach. While stability of the N5+ within the crystal is found to be driven by electronic considerations, the marginal stability of this HEDM is found to be related to a partial softening of its phonon modes.

Pressure-induced stability and polymeric nitrogen in alkaline earth metal N-rich nitrides (XN6, X = Ca, Sr and Ba): a first-principles study

The Fddd-SrN6 structure can transform into P1̄-SrN6, and polymerized to infinite nitrogen chain structures at P = 22 GPa. For BaN6, the Fmmm-BaN6 structure can transform into C2/m-BaN6, and polymerized to N6 ring network structure at P = 110 GPa.

Conduction transition and electronic conductivity enhancement of cesium azide by pressure-directed grain boundary engineering

Alkali metal azides have attracted considerable experimental and theoretical efforts as they are the promising starting materials for the synthesis of polymeric nitrogen, a high-energy-density material. This work reports the...

A Practical Way to Enhance the Synthesis of N8- from an N3- Precursor, Studied by Both Computational and Experimental Methods

Polymeric nitrogen (PN) is a general family of materials containing all-nitrogen molecules or clusters. Although it is rare and challenging to synthesize PN materials, they are attracting increasing scientific attention...