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Metal fluorides are ionic compounds with intriguing properties and a wide range of industrial and technological applications. In this paper, we present the results of an extensive first-principles study of the electronic band structure of nineteen mono-, di-, and tri-fluorides. Four approaches are employed in this study: LDA, pseudopotential and all-electron modified Becke–Johnson (mBJLDA@PP and mBJLDA@AE) potentials, and Yukawa Screened Hybrid Functional (YS-PBE0). The mBJLDA and YS-PBE0 band gaps are in good overall agreement with the available G 0 W 0 results and experimental data, which ensures the reliability of the provided predictions for systems where accurate band gaps are lacking. The LDA and YS-PBE0 upper valence band (UVB) widths are very close to each other, and these results are, in general, slightly smaller than the G 0 W 0 results and experimental data. It is shown that the band gap and UVB width vary with F F distance, and distinct trends are identified. The LDA density of states of the UVB for the alkali and alkaline-earth fluorides are analyzed and compared to the available XPS and XES spectra. It is found that the LDA approach provides accurate results for peak intensities as well as satellite peak positions relative to the main peak. A strong correlation is demonstrated between the adopted crystal structures of the considered fluorides and their bond ionicity. • Four approaches are used to study the electronic structure of 19 metal-fluorides. • For several of the fluorides considered, reliable predictions have been made. • Band gaps and upper valence band widths are found to exhibit clear trends. • The bonding mechanisms of fluorides are discussed in detail. • A correlation is established between bond ionicity and crystal structure. [ABSTRACT FROM AUTHOR]

Assembling two dimensional (2D) materials in vertical heterostructures is one of the main techniques for tuning electronic and optical properties. In most cases, known as van der Waals heterostructures (vdWHs), the interlayer distances are larger than typical covalent bond lengths resulting in weak interlayer interactions. It has been shown that reducing the distance between the layers can significantly alter the properties of separated layers, which is not so noticeable in vdWHs and thus creates a new platform for controlling the physical properties of 2D materials. Motivated by enhanced properties of 2D vertical heterostructures, employing ab-initio calculations based on density functional theory we examined CdO/SnC systems in four different configurations. Our results reveal that in spite of thermodynamic and mechanical stabilities of all considered structures, according to the calculated phonon frequencies, only the structure formed by placing the Sn atom on the O atom and the C atom on the Cd atom is dynamically stable at zero temperature. This structure has an interlayer distance of 2.52 Å which is smaller than the interlayer distance in typical vdWHs. We investigated the electronic and optical properties of this dynamically stable structure utilizing GW approximation and solving Bethe–Salpeter equation. Unlike the monolayer CdO which possesses a single optical absorption peak close to the red light energy, the considered CdO/SnC structure has an optical band gap of 1.14 eV, and it can absorb 13% of incident light in the blue light region. [ABSTRACT FROM AUTHOR]

We calculated electronic structure of Ce 2 Rh 3 Ga 9 , Ce 2 Ru 3 Ga 9 , La 2 Ir 3 Al 9 and Ce 2 Ir 3 Al 9 compounds and we found that Ce 2 Ir 3 Al 9 may exhibit strong topological insulator state according to Z 2 index estimation based on parity algorithm and shape of band structure near Fermi level. The same algorithm shows strong topological insulator state for La 2 Ir 3 Al 9 and Ce 2 Rh 3 Ga 9 compounds, but their band structure near Fermi level is more like semimetallic one. Ce 2 Ru 3 Ga 9 is a normal metal. Our calculations show no magnetic ordering for studied compounds. We also measured the XPS (X-ray Photoelectron Spectroscopy) spectra for these materials, and compared the valence band with simulated spectra, where good agreement was found. Core level states were also investigated and compared with Mulliken population analysis results. According to our measurements and calculations, the highest Ce valence is observed for Ce 2 Ir 3 Al 9 whereas for Ce 2 Rh 3 Ga 9 and Ce 2 Ru 3 Ga 9 the Ce valence is smaller. Hybridization between conduction electrons and 4 f states is very small, and for Ce 2 Ru 3 Ga 9 essentially negligible. [Display omitted] • The first electronic structure calculations with FPLO method of Ce 2 Rh 3 Ga 9 , Ce 2 Ru 3 Ga 9 , La 2 Ir 3 Al 9 and Ce 2 Ir 3 Al 9 have been reported. • The calculations show, that in the case of Ce 2 Ir 3 Al 9 the hour glass-like structure is visible at Γ point, but this structure is visible slightly above the ϵ F. • We found that Ce 2 Ir 3 Al 9 may exhibit strong topological insulator state. • Our calculations show no magnetic ordering for studied compounds. • Moreover, we also found that hybridization of 4 f and conduction electrons is small for Ce 2 Ir 3 Al 9 and Ce 2 Rh 3 Ga 9 and close to zero for Ce 2 Ru 3 Ga 9. [ABSTRACT FROM AUTHOR]