New carbon–nitrogen–oxygen compounds as high energy density materials

Molecular crystals are complex systems exhibiting various crystal structures, and accurately modeling the crystal structures is essential for understanding their physical behaviors under high pressure. Here, we perform an extensive structure search of ternary carbon-nitrogen-oxygen (CNO) compound under high pressure with the CALYPSO method and first principles calculations, and successfully identify three polymeric CNO compounds with Pbam, C2/m and $I\overline{4}m2$ symmetries under 100 GPa. More interestingly, these structures are also dynamically stable at ambient pressure, and are potential high energy density materials (HEDMs). The energy densities of Pbam, C2/m and $I\overline{4}m2$ phases of CNO are about 2.30 kJ/g, 1.37 kJ/g and 2.70 kJ/g, respectively, with the decompositions of graphitic carbon and molecular carbon dioxide and α-N (molecular N₂) at ambient pressure. The present results provide in-depth insights into the structural evolution and physical properties of CNO compounds under high pressures, which offer crucial insights for designs and syntheses of novel HEDMs.