Electronic, optical and sodium K edge XANES in disodium helide: a DFT study.

The ground-state properties of the disodium helide (NaHe) in the cubic structure was calculated using the WIEN2k package within GGA, LDA, and mBJ potentials. From our results, the GGA and LDA predict the material to be semiconductor, while mBJ predicts the material to be insulator. The calculated results from the electronic structure show that NaHe is a direct bandgap semiconductor. Excitonic properties were studied and the results provide Mott-wannier type excitonic behavior of the material. The optical properties for NaHe were studied and its application towards optoelectronic devices has been identified. Also, Na K edge x-ray absorption near edge structure (XANES) for NaHe were computed and discussed. To verify the possibility of formation 2D structure (monolayer) of this compound, phonon calculations were performed. The result indicates that the 2D phase for this compound is dynamically unstable.