Based on first-principles calculations and ab initio molecular-dynamics simulations, the polymerization of the unsaturated cis dinitrogen-difluoride $\left(cis\text{−}{\mathrm{N}}_2{\mathrm{F}}_2\right)$ molecular compound is investigated. The thermodynamic, dynamical, and thermal stabilities of the nitrogen fluorine (NF) system are investigated at conditions of 0–3000 K and 0–200 GPa. The $cis\text{−}{\mathrm{N}}_2{\mathrm{F}}_2$ molecule is a suitable precursor to obtain one-dimensional polymerized nitrogen-fluorine (poly-NF) chains at a pressure above 90 GPa and at a temperature around 1900 K. Importantly, these poly-NF chains can be quenched to ambient conditions, and potentially serve as a high-energy-density material. It has been established that when Al is utilized as a reducing agent, poly-NF chains exhibit a gravimetric energy density of 13.55 kJ/g, which exceeds that of cubic gauche nitrogen (cg-N, 9.70 kJ/g). This is attributable to the presence of both polymerized nitrogen and strong oxidizing F atoms.

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• Energy materials
• Phase transitions
• Polymerization
• Molecules
• Density functional calculations
• Molecular dynamics