First-principle study of the electronic structure of layered Cu₂Se

Copper selenide (Cu₂Se) has attracted significant attention due to the extensive applications in thermoelectric and optoelectronic devices over the last few decades. Among various phase structures of Cu₂Se, layered Cu₂Se exhibits unique properties, such as purely thermal phase transition, high carrier mobility, high optical absorbance and high photoconductivity. Herein, we carry out a systematic investigation for the electronic structures of layered Cu₂Se with several exchange-correlation functionals at different levels through first-principle calculations. It can be found that the electronic structures of layered Cu₂Se are highly sensitive to the choice of functionals, and the correction of on-site Coulomb interaction also has a noticeable influence. Comparing with the results calculated with hybrid functional and G₀W₀method, it is found that the electronic structures calculated with LDA +Ufunctional are relatively accurate for layered Cu₂Se. In addition, the in-plane biaxial strain can lead to the transition of electronic properties from metal to semiconductor in the layered Cu₂Se, attributed to the change of atomic orbital hybridization. Furthermore, we explore the spin-orbit coupling (SOC) effect of Cu₂Se and find that the weak SOC effect on electronic structures mainly results from spatial inversion symmetry of Cu₂Se. These findings provide valuable insights for further investigation on this compound.