Point defects in Dirac semimetal BeN₄ monolayer and their interaction with gas molecules

Point defects in materials may occur during the fabrication process of monolayer materials, or these defects can be created via electron beam irradiation to the perfect crystals. Recently, a triclinic phase of beryllium tetranitride BeN4 was synthesized from elements at similar to 85 GPa pressure and can become a monolayer under ambient conditions. In this study, we have introduced various point defects into the BeN4 monolayer such as Be or N mono vacancy (Be-vac, N-vac), Be-N divacancy (Be-N-vac), antisite defect of Be-N atomic positions and Stone-Wales (SW) defect, and investigated electronic and magnetic changes in the material. It is found that with the Be vacancy, the Dirac cone of the BeN4 monolayer disappears and the Be-vac. monolayer shows semi-metallic properties with overlapping valence and conduction bands. N vacancy induces local magnetic moment (0.797 mu B) to the structure, and the N-vac monolayer has a direct band gap value of 0.172 eV. While the Be-N divacancy turns the structure to metal, the antisite-defected BeN4 monolayer turns into a non-magnetic semiconductor with a band gap value of 0.256 eV. Furthermore, we have introduced bare and defected BeN4 monolayers with CO, CO2, H-2, H2O and O-2 gas molecules and found that these molecules give rise to crucial effects on the electronic and magnetic properties of the materials. While the considered molecules are physisorbed on the bare BeN4 monolayer, the H2O molecule dissociated to OH and H on the N-vac structure, and O-2 molecule strongly binds on N-vac and antisite BeN4 monolayers. Furthermore, we have reported that the antisite BeN4 monolayer may be a good candidate material for hydrogen storage devices with an adsorption energy of 0.355 eV of the H-2 molecule. We believe that our theoretical findings will be beneficial for further experimental and theoretical studies on BeN4 structure.