Characterization of the strain-correlation function in the electronic structure and optical properties of PdBr₂

PdBr₂ is a narrow band gap transition metal halide semiconductor with a van der Waals structure, its unique structure enables the construction of 3D, 2D and 1D structures, and excellent physical chemical properties. However, the structure and physical properties of PdBr₂ are significantly affected by the strain of crystal structure. In order to reveal the mechanism of its influence on the strain regulator, the electronic structure and optical properties of PdBr₂ are regulated by strain, in this paper. The results show that PdBr₂ is a G-M indirect band gap semiconductor in the strain range of −30 % ∼ 35 %. Because of the bottom of the conduction band and the top of the valence band are not distributed in the Brillouin zone in the strain range, the reason for the main factor causing the change of band gap is that the shallow energy level of the conduction band responds significantly to the strain. The fitting results show that there is a $E_g\left(\epsilon \right)=a+\mathrm{b\epsilon }+c{\epsilon }^2+d{\epsilon }^3$ function relationship between the bandgap and strain of PdBr₂, and it can be used to control the electronic structure and optical properties of PdBr₂. State density shows that the electron transition of Pd-4d and Br-4p is significantly affected by strain. These electron transition determines the band gap of PdBr₂, which is the main reason why the band gap changes with strain. The changes of the real part of the dielectric function, refractive index, reflection spectrum and electron energy loss function with strain are similar to the change of band gap with strain. The imaginary part of dielectric function, absorption spectrum, extinction absorption, energy loss function and conductivity increase with the increase of compressive strain, and the performance is more significant in the high energy region. Under the tensile strain, these four optical properties decrease with the increase of strain, and are more significant in the low energy region. The results show that the optical properties of PdBr₂ can be regulated by effectively controlling the strain.