Wyniki wyszukiwania - Biblioteka Nauki

1

Envelope function description of quantum cascade laser electronic states

100%

Wasiak M. , Bugajski M. , Nakwaski W.

Optica Applicata

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2005

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tom Vol. 35, nr 3

651-654

EN

In this paper, we present a natural method of finding wavefunctions and energy levels in quantum cascade lasers. The envelope function approximation has been successfully used for modelling electronic structure in conventional semiconductor lasers. Although calculations in the case of polarized potential are more complicated than in non-polarized wells, it is still possible to obtain quickly reliable results.

2

Electronic structure of CePdAl; experiment and calculations

100%

Głogowski W. , Goraus J. , Ślebarski A.

Materials Science Poland

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2008

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tom Vol. 26, No. 3

729--734

EN

CePdAl exhibits an antiferromagnetic phase below TN = 2.7 K; its physical properties are typical of heavy fermion compounds (specific heat coefficient γ= C/T = 270 mJ/(mol�EK2)). The triangular coordination symmetry of the magnetic Ce ions gives rise to geometrical frustration and leads to an incommensurate antiferromagnetic structure below TN, showing a coexistence of ordered and frustrated Ce moments. The purpose of this work was to discuss electronic structure of CePdAl and its influence on the geometrical frustration in the Kagome-like lattice and the Kondo effect in CePdAl. We present the results of the X-ray diffraction analysis and the XPS Ce 3d core and valence band spectra. We also present the spinpolarized band structure calculations for CePdAl, using the LAPW method.

3

Momentum distributions in positron annihilation with tightly bound electrons in Al

100%

Boroński E.

Nukleonika

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2013

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tom Vol. 58, No. 1

211-214

EN

An approach based on Carbotte, Salvadori and Chiba two-body schemes for calculation of electron-positron (e-p) momentum densities ro(p) for core electrons in solids is developed. The approach allows to avoid such common approximations as the local density approximation (LDA) etc. in determination of ro(p) of deeper atomic shells and reduces the contribution to ro(p) for higher momenta. Thus, the final calculations of the Doppler spectra of annihilation radiation yield lower values for greater momenta than those obtained within the LDA scheme. The exemplary calculations for Al are presented.

4

Positron lifetime calculations for some elements on the base of the GGAPHNC approximation

100%

Boroński E.

Nukleonika

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2010

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tom Vol. 55, No. 1

9-12

EN

In studies of several interesting materials by positron annihilation technique the theoretical values of positron lifetimes in bulk and defected elements are useful. These lifetimes are often calculated within the GGA approximation. In this approximation the results of Arponen and Pajanne calculations for the positron in an electron gas are used. It is known, however, that when using the LDA approximation for the calculations of positron lifetime in real metals, Arponen and Pajanne values yield worse agreement with experimental data than the results obtained on the basis of PHNC formalism. Therefore, in this paper the appropriate PHNC formulas are incorporated into the GGA approximation and the calculations have been performed for some metals: bulk as well as containing monovacancies. The comparison of the lifetimes found in this way to the ones based on the previous method is promising for the applicability of the new algorithm.

5

Electronic structure of Fe2VGa

100%

Goraus J. , Ślebarski A.

Materials Science Poland

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2007

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tom Vol. 25, No. 2

359--362

EN

We present the band structure calculations on the Heusler alloy Fe2VGa which shows a pseudogap at the Fermi level. The compound is found to be nonmagnetic. We observed, however, that an atomic disorder which has been experimentally observed can lead to the behaviour characteristic of the heavy-Fermion compounds. The antisite Fe defects locate the d states forming a narrow d-band at the Fermi level.

6

First-principles calculations to investigate structural, electronic and optical properties of (AlSb)m/(GaSb)n superlattices

80%

Caid M. , Rached D.

Materials Science Poland

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2020

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tom Vol. 38, No. 2

320--327

EN

The structural, electronic and optical properties of (AlSb)m/(GaSb)n (m-n: 1-1, 2-2, 1-3 and 3-1) superlattices are investigated within the density functional theory (DFT) by using the last version of the first principles full potential linear muffin tin orbital method (FP-LMTO) as implemented in LmtART 7.0 code. The exchange and correlation potential is treated by the local density approximation (LDA) for the total energy calculations. Our calculations of the band structure show that the superlattices (n ≠ 1) have a direct band gap Γ-Γ. The optical constants, including the dielectric function ϵ(w), the refractive index n(w) and the reflectivity R(w) are calculated and discussed.

7

The Syntheses, Crystal, Molecular and Electronic Structures of [ReBr3(py)3]0.42[ReBr2(NO)(py)3]0.58, trans-[ReBr4(OPPh3)2] and Orthorhombic Polymorph of mer-cis-[ReBr3(NO)(OPPh3)2]

80%

Machura B. , Dzięgielewski J. , Kusz J.

Polish Journal of Chemistry

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2003

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tom Vol. 77 / nr 5

519-533

EN

[ReBr3(py)3]0.42[ReBr2(NO)(py)3]0.58 (1), trans-[ReBr4(OPPh3)2] (2), [ReBr(NO)(dppe)2]Br (3) and orthorhombic polymorph of mer-cis- [Re(NO)Br3(OPPh3)2] (4) complexes have been synthesized by reactions of monoclinic polymorph of mer-cis-[Re(NO)Br3(OPPh3)2] with pyridine, bis(diphenylophosphino) ethane, 2,2_-bipyridine, 1,10-phenanthroline. The NO group in 1 and 4 is coordinated in a linear way. Due to nitrosyl/bromine compositional disorder, the shortening of Re-NO distance [1.68(5) A] and the elongation of N-O bond length [1.38(10) A] are observed in1. The N-O bond length in 4 is extremely short [0.94(1) A], which results probably from steric interactions of two mutually cis OPPh3 molecules and a large discrepancy of Re-O-P angle values.

8

First Principle Investigations on Electronic, Magnetic, Thermodynamic, and Transport Properties of TlGdX₂ (X = S, Se, Te)

80%

Gautam R. , Kumar A. , Singh R.

Acta Physica Polonica A

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2017

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tom 132

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nr 4

1371-1378

EN

In the present research paper, we investigated spin polarized electronic, magnetic, thermodynamic, and transport properties of thallium gadolinium dichalcogenides TlGdX₂ (X = S, Se, Te) using density functional theory. Electronic structure reveals that all the three compounds are wide band gap semiconductors which are beneficial for good thermoelectric performance. Calculated magnetic moment of TlGdX₂ is found to be in good agreement with available experimental values and mainly dominant by Gd³⁺ ions. Semiclassical Boltzmann transport theory has been used to calculate the Seebeck coefficient and electrical conductivity for the proposed dichalcogenides. Calculated values of the Seebeck coefficient and electrical conductivity are found to be consistent with available experimental values in literature. Thermodynamic properties of TlGdX₂ have also been estimated for the first time and explained on the basic facts.

9

Electronic and optical properties of Mn–S co-doped anatase TiO2 from first-principles calculations

80%

Wu G. , Zheng S. K. , Yan X.

Materials Science Poland

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2016

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tom Vol. 34, No. 1

38--44

EN

The electronic and optical properties of Mn–S co-doped anatase TiO2 were calculated using the plane-wave-based ultrasoft pseudopotential density functional method within its generalized gradient approximation (GGA). The calculated results show that the band gap of Mn–S co-doped TiO2 is larger than that of the pure TiO2, and two impurity bands appear in the forbidden band, one of which above the valence band plays a vital role for the improvement of the visible light catalytic activity. The Mn–S co-doped anatase TiO2 could be a potential candidate for a photo catalyst because of its enhanced absorption ability of visible light.

10

The Synthesis, Spectroscopic Investigation,Crystal and Molecular Structure of the [ReCl2(N2COPh)(2,3'-bpy)(PPh3)2] Complex

80%

Michalik S. , Dzięgielewski J. , Kruszyński R.

Polish Journal of Chemistry

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2006

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tom Vol. 80, nr 5

685-691

EN

The [ReCl2(N2COPh)(2,3'-bpy)(PPh3)2] complex has been obtained in the reaction of [ReCl2(2-N2COPh-N',O)(PPh3)2] with an excess of 2,3'-bipyridyl. The [ReCl2(N2COPh)(2,3'-bpy)(PPh3)2] complex crystallizes in the triclinic space group P-1. The complex was characterized by IR, UV-VIS, and magnetical measurements. The geometries of the complex was optimized with the DFT method.

11

First-principles calculations of electronic structure of rhodochrosite with impurity

80%

He G. , Li K. , Li K. , Guo T. , Li S. , Huang C. , Zeng Q.

Physicochemical Problems of Mineral Processing

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2020

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tom Vol. 56, iss. 1

195--203

EN

The electronic structure of rhodochrosite containing impurity defects is studied by using the first principles density functional theory. The energy band structure, density of states and electronic distribution are calculated for rhodochrosite crystal models with various impurities (e.g., Cu, Ca, Mg, Zn, Fe). This paper discusses the effects of such defects on the electronic structure of rhodochrosite. The calculation results show that the impurity defects have a great impact on the surface electrical properties of rhodochrosite. For example, Ca and Mg impurities reduce the semiconductor width of rhodochrosite. Both Ca and Mg atoms in orbital bonding act as electron donors in which Ca3p and Mg2p orbits provide electrons while O2p orbits receive electrons. Moreover, the more number of valence electrons of Mn is the weaker covalent interaction between Mn and O atoms will be. Meanwhile, decrease of the total energy of rhodochrosite, makes the structure more stable. When Fe, Zn and Cu impurities are contained, the forbidden gap becomes narrower, which improves the conductivity of rhodochrosite. In addition, impurity bands will be formed in the 3d orbits of rhodochrosite as shown in its density of states, and the number of electrons in 3d orbits will increase. This weakens the covalence of O atoms, decreases the population values of O-Mn, increases the bond length, and enhances the ionicity of O-Mn bonds. The impurity of all defects considered in this study have shown an improved conductivity of rhodochrosite, and increased hole concentration of Mn atoms, which will be of great benefit to the adsorption of anionic collectors and enhance the electrochemical properties for rhodochrosite flotation process.

12

Site preference and electronic structure of Mn2RhZ (Z = Al, Ga, In, Si, Ge, Sn, Sb): a theoretical study

80%

Ren Z. , Liu Y. , Li S. , Zhang X. , Liu H.

Materials Science Poland

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2016

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tom Vol. 34, No. 2

251--259

EN

The electronic structure and magnetism of Mn₂RhZ (Z = Al, Ga, In, Si, Ge, Sn, Sb) Heusler alloys have been studied by using first-principles calculations. Three half-metallic ferromagnets, namely, Mn₂RhAl, Mn₂RhGe and Mn₂RhSb have been considered. The calculated equilibrium lattice constant increases with increasing atomic number of Z atoms lying in same column of periodic table. The calculated total magnetic moments M are 2 μ_B/f.u. for Mn₂RhAl and Mn₂RhGa, 3 μ_B/f.u. for Mn₂RhSi, Mn₂RhGe and Mn₂RhSn, and 4 μ_B/f.u. for Mn₂RhSb, which agrees with the Slater-Pauling curve quite well. In all these compounds, except for Mn₂RhSb, the moments of Mn (A) and Mn (B) are antiparallel to each other. The total magnetic moments of the three considered half-metals assume integral values in a wide range of equilibrium lattice parameters.

13

XPS study of RNiSb2 (R = Pr, Nd) compounds

80%

Szytuła A. , Penc B. , Jezierski A.

Materials Science Poland

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2008

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tom Vol. 26, No. 3

759--765

EN

The electronic structure of the ternary RNiSb2 (R = Pr, Nd) compounds, which crystallize in the tetragonal primitive ZrCuSi2-type structure, was studied by the X-ray photoemission spectroscopy. The R3d core-levels and the valence bands were investigated. The results for the PrNiSb2 valence band are compared with the previously calculated density of states. The obtained results indicate that the valence bands are mainly determined by the Ni3d band. The analysis of the XPS spectra of R3d5/2 and R3d3/2 based on the Gunnarsson–Schönhammer model gives the hybridization of the 4f orbitals with the conduction band. The experimental data concerning the valence band of these compounds are compared with the calculations based on the KKR-CPA method. The calculated data for the room temperature (paramagnetic region) give the peaks corresponding to the R4f states at the Fermi level EF = 0. A different distribution of the peaks corresponding to the Ni3d states is observed. For PrNiSb2 three peaks at 2.0, 2.3 and 3.5 eV are observed while for NdNiSb2 a broad maximum between 5.0 and 8.0 eV is visible. The experimental data for PrNiSb2 are in good agreement with the calculated ones while those for NdNiSb2 are not.

14

Electronic structure and magnetic properties of Ce2Pd1-xCoxSi3 and Ce2Pd1-xFexSi3.

80%

Kozłowski G. , Jezierski A.

Materials Science Poland

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2008

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tom Vol. 26, No. 3

693--697

EN

Electronic and magnetic properties of Ce2Pd1–xCoxSi3 and Ce2Pd1–xFexSi3 alloys have been calculated by the TB LMTO-ASA method. The spin polarized calculations indicate that the magnetic moment of Ce2Pd1–xCoxSi3 decreases upon the increase of the concentration x but for Ce2Pd0.5Fe0.5Si3 the value of the magnetic moment has a minimum.

15

Electronic properties of ThCu5Sn and ThCu5In compounds

80%

Werwiński M. , Szajek A.

Materials Science Poland

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2008

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tom Vol. 26, No. 3

724--727

EN

ThCu5In and ThCu5Sn alloys crystallize in an orthorhombic CeCu5Au-type structure with the Pnma space group. Ab-initio band structure calculations have been performed based on the full-potential localorbital (FPLO) method. The calculated densities of electronic states are used to obtain photoemission spectra. The spectra of valence bands are predominated by 3d electrons located on Cu atoms.

16

Ab Initio Study of Structure, Electronic and Magnetic Properties of YFe5 Phase Compound in the DFT Formalism

80%

Gruszka K. , Nabiałek M. , Noga T.

Archives of Metallurgy and Materials

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2016

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tom Vol. 61, iss. 1

369--374

EN

Paper presents results of studies on structural, electronic and magnetic properties of YFe5 compound using density functional theory (DFT) approach. The GGA functional with ultrasoft pseudopotentials were used as implemented in Quantum Espresso software. The structure of YFe5 compound was examined in three different states namely nonmagnetic, antiferromagnetic and ferromagnetic. Also two antiferromagnetic configurations were considered. From the total energy viewpoint the most likely ferromagnetic configuration is favorable. In order to achieve mentioned aims we present projected density of states, electronic band structure and Löwdin population analysis studies results.

17

First-principle calculations for electronic structure and bonding properties in layered Na2Ti3O7

80%

An Y. , Li Z. , Xiang H. , Huang Y. , Shen J.

Open Physics

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2011

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tom 9

|

nr 6

1488-1492

EN

First-principles calculations of Na2Ti3O7 have been carried out with density-functional theory (DFT) and ultrasoft pseudopotentials. The electronic structure and bonding properties in layered Na2Ti3O7 have been studied through calculating band structure, density of states, electron density, electron density difference and Mulliken bond populations. The calculated results reveal that Na2Ti3O7 is a semiconductor with an indirect gap and exhibits both ionic and covalent characters. The stability of the (Ti3O7)2− layers is attributed to the covalent bonding of strong interactions between O 2p and Ti 3d orbitals. Furthermore, the O atoms located in the innerlayers interact more strongly with the neighboring Ti atoms than those in the interlayer regions. The ion-exchange property is due to the ionic bonding between the Na+ and (Ti3O7)2− layers, which can stabilize the interlayers of layered Na2Ti3O7 structure.

18

Structural properties of hypothetical CeBa2Cu3O7 compound from LSDA+DMFT calculations

80%

Łuszczek M.

Materials Science Poland

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2016

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tom Vol. 34, No. 3

617--626

EN

The hypothetical stoichiometric CeBa2Cu3O7 (Ce123) compound, which has not been synthesized as a single phase yet, was studied by the density functional theory (DFT). We utilized a method which merges the local spin density approximation (LSDA) with the dynamical mean-field theory (DMFT) to account for the electronic correlations. The LSDA+DMFT calculations were performed in the high-temperature range. The particular emphasis was put on the pressure-induced changes in the electronic band structure related to strongly correlated 4f states. The computational results indicate the occurrence of a large negative volumetric thermal expansion coefficient near T = 500 K and a trace of a low-volume isostructural metastable state at high temperatures.

19

Under Pressure DFT Investigations on Optical and Electronic Properties of PbZrO₃

80%

Nazir G. , Tariq S. , Afaq A. , Mahmood Q. , Saad S. , Mahmood A. , Tariq S.

Acta Physica Polonica A

|

2018

|

tom 133

|

nr 1

105-113

EN

In this article, density functional theory has been used to investigate the structural and optoelectronic properties of PbZrO₃ (PZO) under pressure from 0 to 350 GPa. In order to achieve ground state structural stability, generalized gradient approximations has been utilized. By studying electronic properties, indirect band-gap nature of PZO appears to change at 15 GPa to direct band-gap. Optical analysis include under pressure responses of real and imaginary parts of dielectric function, optical conductivity, optical absorption coefficient, energy loss function, refractive index, reflectivity and extinction coefficient. Most of the results have been found to be consistent with literature. Study reveals that static dielectric constant and band-gap are in accordance with the Penn model which validates our computed results. Moreover, static dielectric constant and static refractive index directly increases with pressure. Material preserves its positive value of refractive index at all pressures and therefore, it is not a negative index metamaterial. Plasma frequency increases directly with pressure that destabilize the under study material. Our results could be very useful for developing novel optoelectronic devices based on PZO suitable to work under extreme conditions.

20

Structure and electronic properties of Fe-Ti thin films

80%

Smardz K. , Smardz L.

Materials Science Poland

|

2006

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tom Vol. 24, No. 3

827--831

EN

Fe/Ti multilayers (MLs) prepared onto glass substrates using UHV RF/DC magnetron sputtering. Results showed a significant drop of the coercivity measured for the Fe/Ti MLs with decrease in Fe layer thickness - typically from Hc ~ 2.2 kA/m to Hc ~ 0.2 kA/m - observed at a critical Fe thickness dcrit ~ 2.3 nm. Structural studies showed that the deposition of the 0.18 nm - Fe / 0.22 nm - Ti ML at 285 K leads to the formation of an uniform amorphous Fe-Ti alloy thin film due to a strong interdiffusion during the growth process. On the other hand, in-situ annealing of this ML at 750 K for 2 h resulted in the creation of a nanocrystalline phase. Furthermore, in-situ XPS studies showed that the valence band of the nanocrystalline Fe-Ti alloy film is broader compared to that measured for the amorphous phase with the same average composition.