Conclusion We have calculated the structural, electronic, optical and mechanical properties of the two BeCN2 and BeSIN2 ternary compounds belonging to the 4 ?2m symmetry class. With regard to the electronic structure, three exchange and correlation functionalities, namely (CA-PZ LDA), (GGA PBE) and (HSE06), were used. The results found clearly show the consistency of the functional HSE06 compared to the experimental one. These materials have large gaps (~ 5 eV), which allows them to have good Laser Damage Thresholds (LDT) by comparing them with the usual oxides (BBO, LBO, KDP, LiNbO3 …). The Mulliken population analysis shows the existence of two types of bonds which ensure the atomic cohesion in each material, this is due to the fact that the Nitrogen element plays the role of an acceptor, while the other
