Crystal Design Of Green Energetic Beryllium Nitrogen Compounds Under High Pressure

As new generation of high energy density materials?HEDM?,metal nitrogen-rich compounds are widely used in various fields of energetic materials such as high energy density explosives,propellants and gas generators.More and more researchers are paying attention to the research significance and practical value of finding new high energy density materials.We generally require that the performance of high energy density materials be better than that of HMX today?the density is higher than 20 g/cm³,the explosion speed is greater than 9 km per second,and the explosion pressure is greater than 40 GPa?.At the same time,the sensitivity and stability of high energy density materials are similar to that of heat resistance and low sensitivity explosives,such as tri-amino trinitrobenzene.Among many families of energy-containing materials,metal nitrogen-rich compounds are produced by clean and pollution-free nitrogen,which are environmentally friendly clean energy materials.Pressure can change the crystal structure of materials,thus causing changes in physical and chemical properties.The structure under high pressure will be recombined due to the compression of atoms,and then transformed into new materials different from the structure under normal temperature and pressure.Pressure can effectively reduce the chemical barrier of material transformation,so new materials which are difficult to be synthesized under normal pressure can be obtained under pressure.From the perspective,we use the CALYPSO structure search based on particle swarm algorithm search technology from first principles simulation of potential features high pressure behavior of alkaline earth metal beryllium compounds are studied,through the system research crystal structure and electronic properties of beryllium compounds,bonding mechanism and stability,and some innovative research results are obtained.?1?We predicted the novel beryllium nitrogen compound BeN₂,in which two N₄^4-anions with planar zigzag and three branched structures were found.The planar zigzag N₄^4-anion space symmetry group is P2₁/c,with the lowest energy in the pressure range of 0-48 GPa.The N₄^4-anion space symmetry group of the three-branched structure is Cm,with the lowest energy in the pressure range of 48-100 GPa.Be provide 2s electron atoms to change N₄^4-bonding state,and Be empty 2p orbital to accommodate N in the lone pair electrons of the atom,BeN₂ under ordinary conditions of decomposed into Be₃N₂ and N₂,which can release a lot of energy,the energy density were 2.48 kJ/g and2.95 kJ/g,are a kind of potential high energy density materials,at the same time,we studied the stability of that two structures that Be can stable under atmospheric pressure,which are the ideal high energy density materials.?2?We also predicted the new beryllium nitrogen compound BeN₄,in which the planar square N₄^2-ring was found,which was the first N₄^2-ring found in beryllium nitrogen compound crystal.We found that the three structures are two-dimensional P4/nmm-BeN₄,P4/nmm-BeN₄ and Pnma-BeN₄ crystals.The Be atom provides two shell electrons to change the hybridization state between nitrogen atoms,and uses the empty 2p orbital to hold the lone pair electrons of N₄^2-.BeN₄ is also decomposed into Be₃N₂ and N₂ under atmospheric pressure,and its theoretical energy density is as high as 4.577,3.371 and 5.253 kJ/g,respectively.An attractive feature of the structure is that there are a total of six delocalized electrons in the planar square N₄^2-ring,indicating that the structure is aromatic.Through the study of its stability,we found that the two-dimensional structure can be stable at room temperature and pressure,while the three-dimensional crystal needs the pressure of 3GPa to be stable.It is also an ideal high energy density material.