**4. Conclusion**

We study BeSe in zinc blend and NiAs phases using GGA-PBE, LDA, and HSE hybrid. BeSe is a good candidate for photocatalysis material. We estimate the lattice parameters, shear modulus, Young's modulus, Poisson's ratio, average sound velocities, and Debye temperature. The maximum absorption at ultraviolet light is 331,971 cm<sup>1</sup> (335,643 cm<sup>1</sup> ) in zinc blend (NiAs) structure. We perform transverse and longitudinal optical phonon frequencies ωTO and ωLO at Γ point. A frequency gap *Contribution to the Calculation of Physical Properties of BeSe Semiconductor DOI: http://dx.doi.org/10.5772/intechopen.102888*

of 16.06 cm<sup>1</sup> (198 cm<sup>1</sup> ) in zinc blend structure separates longitudinal and transversal optical (acoustic) branches. The reflectivity in the ultraviolet light domain is 0.63% (0.56%) in zinc blend (NiAs) structure. While in the visible light, the reflectivity is 0.43% (0.23%) for the zinc blend (NiAs) phase.
