Wyniki wyszukiwania - Biblioteka Nauki

1

Momentum distributions in positron annihilation with tightly bound electrons in Al

100%

Boroński E.

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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.

2

Envelope function description of quantum cascade laser electronic states

100%

Wasiak M. , Bugajski M. , Nakwaski W.

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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.

3

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

80%

Caid M. , Rached D.

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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.

4

Structure and electronic properties of Fe-Ti thin films

80%

Smardz K. , Smardz L.

Materials Science Poland

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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.

5

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.

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tom 133

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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.

6

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.

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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.

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.

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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.

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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

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.

11

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.

12

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

80%

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

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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.

13

Photoemission study of CeRh(1-x)PdxAl. The effect of Pd doping on the electronic structure

70%

Głogowski W. , Ślebarski A.

Materials Science Poland

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2006

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tom Vol. 24, No. 3

551--555

EN

In view of a contrasting behaviour of Pd-containing and Rh-containing systems, we investigate solid solutions CeRh1-xPdxAl in order to determine the dependence of their electronic properties on the number of the conduction electrons. We present structural and X-ray photoemission spectroscopy (XPS) data for CeRh1-xPdxAl. We also discuss the influence of the number of free electrons in the conduction band on the stability of the crystallographic structure and the occupation number of the f-shell.

14

First-principles LCAO study of phonons in NiWO4

70%

Kuzmin A. , Kalinko A. , Evarestov R.

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nr 2

502-509

EN

The electronic, structural and phonon properties of antiferromagnetic wolframite-type NiWO4 have been studied using first-principles spin-polarized LCAO calculations based on the hybrid Hartree-Fock (HF)/density functional (DFT) scheme. The influence of different percentages of HF contribution, i.e. different correlation strength, on the structure and phonon frequencies has been investigated and compared with the available experimental data.

15

Electronic structure, stability, and strength of Cu-NiAl alloys : experiment and DFT investigation

70%

Zarhri Z.

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tom Vol. 30, No. 2

art. no. e141707

EN

In this study, the copper doping effect on the NiAl structural stability, strength, and electronic structure was investigated. The samples were prepared using induction melting at 2073 K. This material presents good mechanical and physical properties such as high-temperature strength, fatigue or impact, and corrosion resistance which meet technical requirements of many applications. The microstructure of the Cu-doped nickel aluminide was studied using a metallurgical microscope and its lattice parameter was also studied and characterized using an X-ray diffractometer for different concentrations of Cu. The lattice constant of the existing phases was calculated, and it was found that the lattice distortion and gamma prime phase energy have high values allowing the increase of the entropy term of the alloy and subsequently increasing its hardness. From the ab-initio calculation, it was determined that the Cu atoms have the Al sites as a preferred site and prefer to bond with Ni atoms which leads to the improvement of the material hardness. Ab-initio density functional theory was applied to study the formation energy that revealed increasing with Cu amount.

16

Carbon nanotubes functionalized by salts containing stereogenic heteroatoms as electrodes in their battery cells

60%

Zdanowska S. , Pyzalska M. , Drabowicz J. , Kulawik D. , Pavlyuk V. , Girek T. , Ciesielski W.

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tom Vol. 18, nr 4

22--26

EN

This paper concentrates on electrochemical properties of groups of multi-walled carbon nanotubes (MWCNT) functionalized with substituents containing a stereogenic heteroatom bonded covalently to the surface of the carbon nanotube. This system was tested in Swagelok-type cells. The cells comprised a system (functionalized CNT with salts containing S and P atoms) with a working electrode, microfiber separators soaked with electrolyte solution, and a lithium foil counter/reference (commercial LiCoO2 ) electrode. The electrolyte solution was 1 M LiPF6 in propylene carbonate. Using standard techniques (cyclic voltammetry/chronopotentiometry), galvanostatic cycling was performed on the cells at room temperature with a CH Instruments Model 600E potentiostat/galvanostat electrochemical measurements. Methods of functionalization CNT were compared in terms of the electrochemical properties of the studied systems. In all systems, the process of charge/discharge was observed.

17

Dft investigation of a high energy density polynitro compound, 2,2’-Bis(trinitromethyl)-5,5’-azo-1,2,3,4- tetrazole

60%

Lin H. , Zhu S. G. , Chen P. Y. , Li K. , Li H. Z. , Peng X. H.

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tom Vol. 10, no. 3

325--338

EN

A novel polynitro compound, 2,2’-bis(trinitromethyl)-5,5’-azo- 1,2,3,4-tetrazole, was designed and investigated at the DFT-B3LYP/6-31G(d) level. Its properties, such as electronic structure, IR spectrum, heat of formation, thermodynamic properties and crystal structure, were predicted. This compound is most likely to crystallize in the P21 space group, and the corresponding cell parameters are Z = 2, a = 5.46 Å, b = 9.72 Å, c = 14.05 Å, α = 90°, β = 90°, γ = 90°. In addition, the detonation velocity and pressure were also estimated by using the empirical Kamlet-Jacobs equations, and were predicted to be 8.28 km/s and 31.61 GPa respectively. The oxygen balance of this compound is +13.79%, which indicates that it could serve as an oxidizer. Bond dissociation energy calculations show that the C(13)-N(21)O2 and C(14)-N(30)O2 bonds are the locations of thermal decomposition and that this compounds meets the thermal stability requirements as an exploitable explosive. Keywords: polynitro, electronic structure, thermodynamic properties, crystal structure, detonation performance, stability.

18

Mössbauer study of a tetrakis (pentafl uorophenyl) porphyrin iron (III) chloride in comparison with the fluorine unsubstituted analogue

60%

Kaczmarzyk T. , Dziedzic-Kocurek K. , Rutkowska I. , Dziliński K.

Nukleonika

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2015

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tom Vol. 60, No. 1

57--61

EN

Mössbauer investigations, in association with density functional theory (DFT) calculations, have been conducted for the molecular and electronic structures of iron (III) [tetrakis (pentafl uorophenyl)] porphyrin chloride [(F20TPP)Fe:Cl], as a Fe(III)-tetraphenylporphyrin complex containing chloride axial ligand and substituted hydrogen atoms by fl uorine ones in the four phenyl rings, in comparison with its fl uorine unsubstituted analogue [(TPP)Fe:Cl]. It was found that the parameters of Mössbauer spectra of both complexes are close to one another, and correspond to the high-spin state of Fe(III) ions, but they show the different temperature dependence and the quadrupole doublets in Mössbauer spectra show different asymmetry at low temperatures. Results of DFT calculations are analyzed in the light of catalytic activity of the halogenated complex.

19

Electronic structure of f-electron intermetallic compounds studied by positrons

60%

Samsel-Czekała M. , Kontrym-Sznajd G. , Biasini M.

Materials Science Poland

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2006

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tom Vol. 24, No. 3

611--615

EN

The electronic structure of isostructural rare-earth intermetallic compounds TmGa3, ErGa3, and CeIn3 has recently been studied by measurements of two-dimensional angular correlations of annihilation radiation (2D ACAR) spectra. On the example of these systems we show what kind of information can be exploited from such spectra, i.e. from line projections of the electron-positron (e-p) momentum density ?(p). By applying various tomographic techniques, we check how these algorithms can affect reconstructed 3D momentum densities and Fermi surfaces (FS). We confirm that for all these systems in the paramagnetic phase the f-electrons are fully localized and their FS's are similar. TmGa3 and ErGa3 exhibit the FS nesting feature, in agreement with their magnetic structure, which is not a case in CeIn3.

20

Complex Magnetic Phenomena in f-Electron Intermetallic Compounds

60%

Szytuła A.

Materials Science Poland

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2006

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tom Vol. 24, No. 3

737--751

EN

In the paper various aspects of magnetic properties of lanthanide and actinide intermetallic compounds are discussed. The first part deals with 1:2:2: stoichiometry compounds. The magnetic ordering - type in the function of temperature is discussed. Then the electronic structure of these compounds is presented. The third part concentrates on magnetically hard intermetallics