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Correlations in Hexagonal Lattice Systems - Application to Carbon Nanotubes

100%
Czajka K., Maśka M.
Acta Physica Polonica A
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2004
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vol. 106
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issue 5
703-707
EN
We present exact diagonalization studies of two-dimensional electron gas on hexagonal lattice. Using Lanczös method we analyze the influence of the Coulomb correlations on the density of states and spectral functions. Choosing appropriate boundary conditions we simulate the geometry of a single wall carbon nanotube. In particular, integration over the boundary condition in one direction and summation in the other one allows us to perform cluster calculations for a tube-like system with a finite diameter and infinite length.
2
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Electronic States in Type-II Superlattices

80%
Machowska-Podsiadlo E., Bugajski M.
Acta Physica Polonica A
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2009
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vol. 116
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issue S
S-65-S-68
EN
In this paper the electronic states in type-II superlattices are demonstrated. Band dispersions of InAs/GaSb periodic structure were calculated with the respect of the light and the heavy holes states mixing at InAs/GaSb interfaces. The effect of narrow energy band gap of InAs was taken into account and the wavelengths corresponding to optical transitions in the superlattice were presented.
3
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Interatomic Pair Interaction in Liquid Transition Metals

80%
Dubinin N.
Acta Physica Polonica A
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2009
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vol. 115
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issue 4
783-785
EN
The Wills-Harrison pair interaction is investigated for liquid Fe on the base of the introduced relation between parameters of the model pseudopotential and d-electron characteristics. It is shown that the procedure suggested leads to the significant shift of the first minimum of the pair potential and increases the softness of its repulsive part.
4
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Derivation of von Weizsäcker Equation Based οn Green-Gauss Theorem

80%
Romanowski Z., Krukowski S.
Acta Physica Polonica A
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2009
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vol. 115
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issue 3
653-655
EN
A simple and short derivation of von Weizsäcker equation for kinetic energy functional is presented. The derivation is based on the Green-Gauss theorem and is valid for one-electron systems. In the proof the asymptotic behavior of wave function for the finite systems was used. Two results important for kinetic energy functional evaluation are also derived as consequences of the Green-Gauss theorem.
5
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Electron and Exciton Quasi-Stationary s-States in Open Spherical Quantum Dots

80%
Tkach M., Seti J., Voitsekhivska O.
Acta Physica Polonica A
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2012
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vol. 122
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issue 1
207-211
EN
The theoretical calculation of spectral parameters of electron and exciton quasi-stationary s-states in open spherical quantum dot is performed within the effective mass approximation and rectangular potentials model. The conceptions of probability distribution functions (over quasi-momentum or energy) of electron location inside of quantum dot and their spectral characteristics: generalized resonance energies and widths are introduced. It is shown that the generalized resonance energies and widths, obtained within the distribution functions, satisfy the Heisenberg uncertainty principle for the barrier widths varying from zero to infinity. At the same time, the ordinary resonance energies and widths defined as complex poles of scattering S-matrix, do not satisfy it for the small barrier widths and, therefore, are correct only for the open quantum dots with rather wide potential barriers.
6
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Ab Initio Investigation on the Effect of Transition Metals Doping and Vacancies in WO₃

80%
Mansouri M., Mahmoodi T.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1
8-14
EN
We did a density functional theory spin-polarized calculation based on pseudopotential method on the effect of both vacancy and substitutional impurity in the tungsten tri-oxide lattice. We investigated oxygen and tungsten vacancies and for substitutional dopants we used palladium (Pd), platinum (Pt) and gold (Au) atoms with the formula A_xW_{1-x}O₃ and x=0.125, 0.25, 0.375, 0.5. We obtained electronic band structure, density of states and magnetization of defected and doped WO₃. The results show that in the presence of tungsten vacancy, WO₃ acts as a semiconductor with an indirect band gap while oxygen vacancy induces a metallic behavior for WO₃. Besides, for Pt and Pd the location of trap states lead to photoexcited hole capturing, which can improve photocurrent but for Au dopant, the trap states occur in the middle of the band gap as active recombination centers. Furthermore, both kind of vacancies and Pt dopant can induce magnetization in all values of x, while Pd and Au are less efficient in inducing magnetization.
7
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Structural Design and Characterization of BaMg_{x}Co_{2-x}Fe_{16}O_{27} Hexaferrites Based on ab initio Computations

70%
Bakhtiari M., Nabiyouni G., Besharati-Seidani A.
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vol. 126
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issue 6
1288-1292
EN
Structural design of barium hexaferrites BaMg_xCo_{2-x}Fe_{16}O_{27} (x=0.0, 1, 2) has been studied, and the magnetic and electronic structure of that has then been investigated using first principle total energy calculation. All calculations are based on the density functional theory. In order to improve the description of strongly correlated 3d electrons of iron, the general gradient approximation plus Hubbard U (GGA+U) method is used. We found that in the lowest energy configuration Mg and Co ions preferentially occupy the 6g sites. With the increase of Mg content x, the energy gap of BaMg_xCo_{2-x}Fe_{16}O_{27} increases but the lattice constant of unit cell decreases. The magnetic moment of the unit cell for Mg content x=0, 1, and 2 are calculated to be 52, 49 and 46 μ_{B}/cell, respectively, in agreement with previous experimental results. The substitutions of Mg and Co at the BaFe_2^{2+}Fe_{16}^{3+}O_{27} decrease electrical conductivity and transit it from a half-metal to semiconductor material. Based on our calculations on electronic band structure, the BaFe_2Fe_{16}O_{27} (BFFO) is a weak half-metal, but BaMg_2Fe_{16}O_{27} (BMFO), BaMgCoFe_{16}O_{27} (BMCFO) and BaCo_2Fe_{16}O_{27} (BCFO) are semiconductors. The electrical resistivity increases by increasing Mg and Co contents due to increase in porosity which prevents the hopping of charge carriers.
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