AB INITIO CALCULATION OF ELECTRONIC ENERGY SPECTRUM OF METALLIC TIN ULTRATHIN NANOFILMS
The results of ab initio computer modeling of the electronic structure of metallic tin (β-Sn) ultrathin nanofilms of various thickness are presented. The spectra of total and local partial densities of electronic states have been calculated using the linearized augmented plane wave (LAPW) method in the approximation of layered superlattice. The M4,5 X-ray absorption near-edge fine structure spectra for the surface layers of nanofilms have been calculated by simulating the supercell, using the "core-hole" approximation. Convergence to the some ultimate form with an increase of the nanofilm thickness is obtained for all types of spectra. It is shown, that the nanofilm of 10 unit cell thickness is sufficient extended, and its results of band structure calculation can be regarded as a model, describing modification of features of tin under moving from the bulk of single crystal towards its surface. It has been shown that quite at the distance ~ 5 Å from surface of material the DOS spectra of the appropriate layers appear to be close to the DOS of bulk specimen. The spectrum of total density of states of atom on the nanofilm surface is characterized by the presence of the high sharp maximum at –7 eV. XANES M4,5 spectrum also demonstrates an appearance of the sharp maximum near the Fermi level. Effect of the "core-hole" approximation on the result of calculation of XANES spectrum of the surface atom of nanofilm has been studied. Unlike the bulk sample, accounting for core hole in case of a nanofilm changes the form of a spectral curve only slightly. The reason for this is, most likely, the smaller value of the perturbation introduced by the core hole, in comparison with the perturbation introduced by the surface of the nanofilm.
Calculations were carried out at the computing facilities of the Data Processing Center (DPC) of VSU.
This work was financially supported by the RFBR grant within the framework of the scientific project No. 16-32-00860 mol_a, and the Voronezh Region government in the framework of the scientific project No. 16-42-360612 p_a.
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