Predicting the crystal structure of [Formula: see text] high energy density material using ab initio evolutionary...

Area of Science:

• Materials Science
• Computational Chemistry
• Solid-State Physics

Background:

• Polymeric nitrogen ([Formula: see text]) is a high energy density material (HEDM).
• The crystal structure of [Formula: see text] has remained unknown due to experimental challenges.
• Previous studies suggested a [Formula: see text] symmetry for the [Formula: see text] cation.

Purpose of the Study:

• To determine the crystal structure of [Formula: see text].
• To validate the ab initio evolutionary prediction method for HEDMs.
• To understand the factors contributing to the stability and instability of [Formula: see text].

Main Methods:

• Ab initio evolutionary crystal structure prediction.
• Computational analysis of electronic structure and phonon modes.

Main Results:

• The crystal structure of [Formula: see text] was successfully predicted.
• The predicted structure confirmed the [Formula: see text] symmetry of the [Formula: see text] cation.
• Electronic factors were identified as key to the cation's stability within the crystal.
• Partial softening of phonon modes was linked to the material's marginal overall stability.

Conclusions:

• Ab initio evolutionary prediction is a valid approach for determining the structures of unstable HEDMs.
• The crystal structure of [Formula: see text] has been elucidated.
• Understanding the stability mechanisms is crucial for the future development of polymeric nitrogen materials.