Structural stability of polymeric nitrogen: A first-principles investigation.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Polymeric nitrogen is a target for high energy density materials due to its potential.
• Understanding the stability of different nitrogen allotropes under pressure is crucial for synthesis and application.

Purpose of the Study:

• To evaluate the thermodynamic, mechanical, and dynamical stabilities of candidate polymeric nitrogen structures.
• To determine the pressure ranges for the stability of these structures.
• To identify novel, stable polymeric nitrogen phases.

Main Methods:

• Ab initio calculations based on density-functional theory (DFT).
• Analysis of stability across a pressure range of 0 to 360 GPa.
• Comparison of various candidate polymeric nitrogen structures.

Main Results:

• Cmcm, A7, rcg, cg, BP, P2(1)2(1)2(1), and Pba2 structures are identified as thermodynamically and dynamically favorable over others (sc, ch, LB, cw).
• BP, Pba2, and P2(1)2(1)2(1) exhibit lower enthalpies than cg above 170 GPa, indicating novel stability.
• The P2(1)2(1)2(1) phase can transform to the cg structure below 60 GPa.

Conclusions:

• Several polymeric nitrogen structures show promise as stable high energy density materials.
• A new phase transition pathway for nitrogen under increasing pressure is proposed: molecular N(2) to cg (47 GPa), then to Pba2 (170 GPa), and finally to P2(1)2(1)2(1) (307 GPa).