Papers by Keyword: Ab Initio Calculation

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Authors: M.S. Blanter, V.V. Dmitriev, Andrei V. Ruban
Abstract: t is common knowledge that interstitial-interstitial interaction influence on the Snoek relaxation. We used a computer simulation of this effect in the Nb-O alloy to test the adequacy of various models of the O-O interaction and clarify the mechanism of this effect The energy calculations in the first twelve coordination shells have been performed by the projector augmented-wave (PAW) method as implemented in the Vienna ab initio simulation package (VASP). The energies have been calculated in different ways which vary in the method of determination the energy of non-interacting O-O pairs. The energies calculated on the various variants are similar but in one case there is O-O repulsion in all first twelve coordination shells, whereas in another one can see attraction in four of twelve shells. Internal friction Q-1 was calculated as a sum of the contributions from individual interstitial atoms in different environments, each of which being assumed to be the Debye function. It is assumed that long-range interaction of oxygen atoms affects the distribution of these atoms and the energy of each interstitial atom in the octahedral interstices before a jump and after a jump. The Monte Carlo method is used for simulating short-range order of interstitial atoms and for calculating values of energy changes. Comparison of the calculated temperature and concentration dependence of the Snoek peak with the published data showed that the PAW supercell calculation of the O-O interactions in Nb describes the behavior of the interstitial solid solution adequately. It proves also that the impact of interstitial atom concentration on the Snoek relaxation is connected to the mutual attraction of these atoms.
Authors: Anton Gnidenko
Abstract: Quantum-mechanical calculations were performed for investigation of tensile strength for WC/Co/WC systems with the thickness of the cobalt interlayer of 3 and 7 atomic layers. It has been shown that the cobalt interlayer increasing leads to decreasing of the tensile strength from 17 GPa to 14 GPa. In addition, vacancy-type defect formation reduces the tensile strength of about 2 times.
Authors: Yoshitaka Umeno, Kuniaki Yagi, Hiroyuki Nagasawa
Abstract: We carry out ab initio density functional theory calculations to investigate the fundamental mechanical properties of stacking faults in 3C-SiC, including the effect of stress and doping atoms (substitution of C by N or Si). Stress induced by stacking fault (SF) formation is quantitatively evaluated. Extrinsic SFs containing double and triple SiC layers are found to be slightly more stable than the single-layer extrinsic SF, supporting experimental observation. Effect of tensile or compressive stress on SF energies is found to be marginal. Neglecting the effect of local strain induced by doping, N doping around an SF obviously increase the SF formation energy, while SFs seem to be easily formed in Si-rich SiC.
Authors: M.V. Magnitskaya, E.T. Kulatov, A.A. Titov, Y.A. Uspenskii, E.G. Maksimov, S.V. Popova, V.V. Brazhkin
Abstract: We report on ab initio density-functional calculations of a novel spintronics-related compound CrGa2Sb2 recently synthesized under high pressure. The effect of Cr deficiency on the electronic, magnetic and optical properties of CrGa2Sb2 is considered. New X-ray structural measurements up to high pressure of 9 GPa are presented.
Authors: Mudra R. Dave, A.C. Sharma
Abstract: The electronic and optical properties of bimetallic single atomic linear chains of Au-Pd have been investigated within Density functional theory frame work. Dielectric matrix has been computed within random phase approximation for atomic chains with different compositions. The results of bimetallic atomic chains of Au-Pd are compared with the pristine Au and Pd atomic chains. It has been found that doping the pristine chains affects the real and imaginary part of dielectric function which is greatly dependent on the composition of bimetallic chains.
Authors: Vsevolod I. Razumovskiy, Pavel A. Korzhavyi, Andrei V. Ruban
Abstract: Self-diffusion of the metal and carbon atoms in TiC and ZrC carbides is studied by first principles methods. Our calculations yield point defects energies, vacancy jump barriers and diffusion pre-factors in TiC and ZrC. The results are in reasonable agreement with the available experimental data and suggest that the self-diffusion mechanism for metal atoms in these carbides may involve nearest-neighbor vacancy pairs (one metal and one carbon vacancy).
Authors: Jing Wen, Chun Ying Zuo, Cheng Zhong
Abstract: Motivated by the widely discussed Ag doped ZnO and the lack of follow-up reports about the realization of p-n junctions, we calculated the electronic structures and optical properties of pure, Ag-doped and Ag-F codoped ZnO based on the density-functional theory. It was found that Ag doped ZnO shows p-type conduction character. But there are some unstable factors and self-compensations in this structure. We also calcualted the formation energy and ionization energy of the impurity for Ag-F codoped ZnO. It was found that incorporating the reactive donor F into Ag doped ZnO system, not only enhances the Ag acceptor solubility, but also gets a shallower Ag acceptor energy level in the band gap. In addition, we analyze the imaginary part of the dielectric function, reflectivity and absorption coefficient for pure ZnO and Ag-F codoped ZnO. Compared with the pure ZnO, the remarkable feature for Ag-F codoped ZnO is that there is a strong absorption in the visible-light region, which indicates that it could be taken as a potential candidate for a photocatalytic material.
Authors: Oliver Kirstein, Jian F. Zhang, Erich H. Kisi, D.P. Riley
Abstract: The ternary carbide Ti3SiC2 is the archetype of MAX phases. To date, MAX phases have proven difficult to synthesize as sufficiently large single crystals from which single crystal elastic constants might be obtained. Therefore, the elastic properties not only of Ti3SiC2 but other MAX phases are extensively studied by ab initio methods. Recently single crystal elastic constants were experimentally determined for the first time using neutron diffraction. The experiment revealed extreme shear stiffness which is not only quite rare in hexagonal materials but also strongly contradicts the predictions of all published MAX phase elastic constants from ab initio calculations. In the present paper we would like to show that such shear stiffness can possibly be supported by ab initio calculations and the calculated phonon dispersion along high symmetry directions.
Authors: E.T. Kulatov, A. Titov, Y.A. Uspenskii
Abstract: Energy difference between the ferromagnetic and antiferromagnetic collinear orderings has been calculated for the uniform and dimer Mn-pair geometries in order to find the ground state distribution of the Mn atoms in InSb (As) hosts. We find the preference of the dimer ferromagnetic configuration of Mn dopants and an importance of optimizing the atomic site positions. The frequency-dependent optical and magneto-optical properties, namely the reflectivity, the electron energy loss spectra, on-and off-diagonal conductivity tensor and the polar Kerr effect, are calculated for comparison with available experimental data. Our calculated MO resonance in In1-xMnxSb (x=1.56%) are found to be in good agreement with corresponding experimental MO spectra. The origin of the large Kerr rotation is discussed.
Authors: Mikhail A. Zagrebin, Vladimir V. Sokolovskiy, Vasiliy D. Buchelnikov
Abstract: In this work the magnetic properties (exchange parameters, magnetic moment of non-stoichiometric Ni–Mn–Ga Heusler alloys with structural disorder by the help of ab initio calculations have been performed. Theoretical composition dependences of the total magnetic moment are in qualitative agreement in qualitative agreement with experimental data. Calculations of exchange parameters show that interactions between the Mn atoms in regular positions and Mn atoms in Ni and Ga positions are antiferromagnetic.
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