Electronic Structure Characteristics of Complex Chalcogenides, Halides, and Oxides from Quantum-Mechanical Calculations

Introduction . Modern quantum and optoelectronics, as well as nonlinear optics, place high demands on the physical and chemical properties of the materials used. This necessitates, among other things, the search for new materials that possess the properties required for a given application. At the same time, this approach can complicate the composition and crystal structure of the resulting compounds. The electronic structure of complex compounds determines their electrical, optical, magnetic, and chemical properties. These properties are unique to each compound. However, it is known that different compounds that are similar in some important parameters, for example isoelectronic ones, exhibit similarities in the structure of their electronic shells. The accumulation of such information on individual compounds and their groups necessitates generalizing the data obtained. The research objective is to consider some general characteristics of the electronic structure exhibited by groups of different compounds (chalcogenides, halides, and oxides). Materials and Methods. The subject of study was three groups of compounds: chalcogenides Tl 3 TaS 4 , Tl 3 PS 4 , Sn 2 P 2 S 6 , InPS 4 , Cu 2 CdGeS 4 , Ag 2 CdSnS 4 , Ag 2 HgSnS 4 , halides Cs 2 HgX 4 X = Cl, Br, I, group APb 2 Br 5 A = K, Rb, and oxides La 2 Zr 2 O 7 , Nd 2 Zr 2 O 7 , Sm 2 Zr 2 O 7 , Eu 2 Zr 2 O 7 , Gd 2 Zr 2 O 7 . The research method involved quantum-mechanical calculations within the framework of density functional theory with various exchange-correlation potentials. Potentials were used that allowed for strong correlations between d- and f-electrons and yield a band gap value close to the experimental value. Results . Quantum-mechanical calculations of the electronic state densities and optical characteristics of a number of chalcogenides, halides, and oxides were performed. Partial and total electron densities of states (DOS) were presented. The total density of states was compared with experimental X-ray photoelectron spectra (XPS). The validity of the calculation results was confirmed. The top of the valence band was formed by the p-states of the most electronegative elements (S, Se, Te, Br, O), whereas the bottom of the valence band was formed by the s-states of these same electronegative elements. Discussion. Based on the calculations, general conclusions were drawn regarding the similarities in the valence band structure of the compounds considered. Using the compound Tl 3 TaS 4 as an example, it was shown that in a solid, compared to the energies in a free atom, the binding energy of the levels for electronegative elements was significantly reduced, while for electropositive elements, it was increased. A rare-earth element (using Eu 2 Zr 2 O 7 as an example) significantly altered the electron-energy structure, such that the electron states of the rare-earth element (4f-, 5p-) and the 5s-states of europium (Eu) altered the structure of the valence band of pyrochlore (Eu 2 Zr 2 O 7 ). The calculated total and partial DOS were compared with experimental X-ray and X-ray photoelectron spectra, which confirmed the accuracy of the calculations. However, the calculated DOS curves contained numerous fine-structure elements that were obscured by instrumental distortion in the experimental curves. Thus, the calculation complemented the experiment very well, providing a more detailed picture of the electron-energy structure of the studied compounds. Conclusion. The research objective was achieved: some general characteristics of the electronic structure exhibited by groups of different compounds (chalcogenides, halides, and oxides) were examined. The problems of identifying the states that determined the features of the electronic structure and optical characteristics of the studied groups of compounds were solved. This research can be used in the modeling of new materials with desired properties.