First-principles calculations to investigate optical properties of topological semimetal MX compounds (M = Ti, Zr, Hf and X = S, Se, Te)

In this study, the first-principles calculation was used to explore the optical properties of MX (M = Ti, Zr, Hf, and X = S, Se, Te) compounds in light of their newly discovered unique electronic properties over a broad energy range. The influence of each orbital (s, p, and d) was studied by comparing the imaginary and real spectra of dielectric functions with the electronic properties of these compounds. The d-orbital of transition metals has a major impact on the absorption performance of all these compounds. In negative regions of the real spectra, a very high intensity of reflectivity was observed. The high peaks of energy loss along x, y, and z components are linked to plasmons and in good agreement with real (Re_ii (ω) =0) and imaginary (Img_ii (ω)≈0) spectra values. For transition metal M (i.e., Ti, Zr, and Hf), when the X element is changed from S to Te, a significant shift from higher to lower energy has been observed in the imaginary, real, reflectivity, and energy loss spectra of the x, y, and z components, respectively.