Papers by Stepan Syrotyuk
Computational Problems of Electrical Engineering
Atthe first stage, the structureof theZnSe crystal doped with chromium atoms (ZnCrSe)has been fou... more Atthe first stage, the structureof theZnSe crystal doped with chromium atoms (ZnCrSe)has been found by optimization procedure. At the second stage, the electronic properties of this material have been evaluated within the two approaches. The exchange-correlation functionals used here are based on the generalized gradient approximation (GGA) and the hybrid functional PBE0. The GGA approach provides the metallic state for electrons with the spin up, and for opposite spin orientation the material ZnCrSe bahaves as semiconductor, with the band gap of 2.48 eV. The hybrid functional approach also gives a gapless state for a spin up electron states, and for a spin down it provides the forbidden gap value of 2.39 eV. The magnetic moment of the unit cell, found with the two functionals, is the same and equals to 4 Bμ(Bohr magnetons). So, the calculations with the two exchange-correlation functionals provide the prediction of half-metallic properties of the ZnCrSe material, which is an intere...
Computational Materials Science
Radiation Measurements, Jul 1, 2016
The thermalization length distribution of electrons over their kinetic energy in a conduction ban... more The thermalization length distribution of electrons over their kinetic energy in a conduction band is calculated on the basis of the data on the electron effective mass, density of states in conduction band, dielectric permittivity and energy of longitudinal optical phonons. The method of modeling of a recombinational luminescence intensity dependence on the nanoparticle size is proposed on the basis of the assumption that the contribution to a recombinational luminescence gives only those charge carriers which in the result of thermalization did not reach a near-surface layer of nanoparticles. Using such the approach the theoretical dependence of recombinational luminescence intensity on the nanoparticle size for LaPO 4 and LuPO 4 are calculated. The revealed correlation of experimental and theoretical dependences confirms that the commensurability of electron thermalization length with nanoparticle size is the main reason of the sharp decrease of X-ray excited luminescence intensity when the nanoparticle size decreases.
Condensed Matter Physics, 2015
The electronic energy band spectra of the alkali metal chalcogenides M 2 A (M: Li, Na, K, Rb; A: ... more The electronic energy band spectra of the alkali metal chalcogenides M 2 A (M: Li, Na, K, Rb; A: O, S, Se, Te) have been evaluated within the projector augmented waves (PAW) approach by means of the ABINIT code. The Kohn-Sham single-particle states have been found in the GGA (the generalized gradient approximation) framework. Further, on the basis of these results the quasiparticle energies of electrons as well as the dielectric constants were obtained in the GW approximation. The calculations based on the Green's function have been originally done for all the considered M 2 A crystals, except Li 2 O.
2012 IEEE International Conference on Oxide Materials for Electronic Engineering (OMEE), 2012
ABSTRACT The electron energy bands and densities of states have been calculated within the projec... more ABSTRACT The electron energy bands and densities of states have been calculated within the projector augmented waves (PAW) formalism. The PBE exchange-correlation functional gives the absence of the gap contrary to the experiment. The account of the exact exchange substantially improves the results for direct and indirect interband gaps.
Functional Materials, 2013
The European Physical Journal B, 2015
The journal of physical chemistry. A, Jan 14, 2009
The electronic structure of liquid boron and cluster formation in expanded liquid boron have been... more The electronic structure of liquid boron and cluster formation in expanded liquid boron have been investigated with first-principles molecular dynamics simulations. The calculated electronic density of states (DOS) exhibits a metallic feature, while liquid boron is known experimentally to be semiconductive. Since the DOS is not very sensitive to density, the electronic states near the Fermi level will consist mainly of dangling bonds, which explains the difference between the calculated and experimental results. Many types of clusters are formed in expanded liquid boron. This formation occurs in a very different way from that at low temperatures because expanded liquid boron has a high temperature and pressure that are close to the liquid-gas critical point. As the density is reduced, the coordination number in boron clusters decreases to about 2, indicating that the cluster geometry tends to be one- rather than two-dimensional, which is the most stable form at low temperatures. In ...
Contribution to a conf. proceeding (book/online)
Journal of Physical Studies
Отримано 24 жовтня 2012 р.; в остаточному виглядi 24 вересня 2013 р.) Дослiджено остовно-валентну... more Отримано 24 жовтня 2012 р.; в остаточному виглядi 24 вересня 2013 р.) Дослiджено остовно-валентну люмiнесценцiю кристала CsCl. Розраховано електронну енергетичну структуру кристала CsCl з використанням методiв LDA та GW. Зроблено порiвняння розрахункових та експериментальних параметрiв остовно-валентної люмiнесценцiї кристала CsCl. Ключовi слова: параметри енерґетичної структури, зонна структура, парцiальна густина станiв.
Solid State Phenomena, 2013
The spin-resolved electronic energy bands and partial and total density of states of cadmium oxid... more The spin-resolved electronic energy bands and partial and total density of states of cadmium oxide doped with Sc, Ti and Cr have been evaluated by means of the ABINIT code. The strong electron correlations of Cd 4d and transition element 3d states have been taken into account. It was found that the CdScO and CdTiO crystals are paramagnetic and CdCrO shows the ferromagnetic ordering.
Condensed Matter Physics
The spin-resolved electronic energy band spectra, as well as partial and total density of electro... more The spin-resolved electronic energy band spectra, as well as partial and total density of electronic states of the crystal AlN, doped with Cr, Mn and Fe, have been evaluated within the projector augmented waves (PAW) approach by means of the ABINIT code. The Hartree-Fock exchange for correlated electrons is used to describe the correlated orbitals in the PAW framework. The calculated one-electron energies for electrons of spin up and down are very different. We have found that all the considered crystals are ferromagnetic.
Physica Status Solidi (c), 2010
Electronic energy bands of ZnS, ZnSe, and ZnTe crystals evaluated within the mixed basis approach... more Electronic energy bands of ZnS, ZnSe, and ZnTe crystals evaluated within the mixed basis approach with using the core Bloch states and plane waves. The exchange-correlation potential has been derived from the new exchange-correlation-energy functional including the density gradient corrections and the intra-atomic Coulomb term U. The calculated energy band structure parameters of the crystals show an improvement compared with the LDA results. The semicore Zn 3d state energies are closer to experimental data than those obtained within the LDA approach. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Physica Status Solidi B-basic Solid State Physics, 1996
The orthonormalized core Bloch states for crystalline copper have been obtained by means of the u... more The orthonormalized core Bloch states for crystalline copper have been obtained by means of the unitary rotation matrix. This matrix depends on anoverlap matrix which is evaluated on non-orthogonal core Bloch functions. We evaluate the orthogonalization matrix in two ways. The first one consists in evaluation of the orthogonalization matrix exactly by iteration. The second approach is perturbative. The comparison of the numerical results of these two approaches allows us to conclude that the orthogonalization of core Bloch functions for crystalline copper should be done by means of aunitary rotation matrix, which is evaluated up to fifth order with respect to the overlap matrix.
Physica Status Solidi B-basic Solid State Physics, 1997
ABSTRACT The formula for calculating the spectrum gradient gk = gradk E(k) at an arbitrary point ... more ABSTRACT The formula for calculating the spectrum gradient gk = gradk E(k) at an arbitrary point k in the Brillouin zone has been derived on the basis of the new completely orthogonalized plane wave formalism (COPW). This important physical quantity has been obtained within the COPW basis for the first time. It displays a true plane wave basis limit.
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Papers by Stepan Syrotyuk