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1
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Effect of the Positron Distribution on the Electron-Positron Momentum Density Calculated for SiC

100%
Rubaszek A.
Acta Physica Polonica A
|
2008
|
vol. 113
|
issue 5
1501-1506
EN
To interpret positron annihilation data in solids in terms of the electron momentum density, both the electron-positron interaction and positron distribution have to be considered explicitly. In the present work the influence of the shape of the positron wave function on the calculated electron-positron momentum density in elemental SiC is discussed. It is shown that the form of the positron distribution in the Wigner-Seitz cell has a considerable effect on the resulting annihilation characteristics. Calculations were performed for SiC of 3C diamond structure within the linear muffin-tin orbital-atomic spheres approximation method.
2
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Electron-Positron Momentum Densities for Electrons from Individual Core Levels

100%
Rubaszek A.
Acta Physica Polonica A
|
2005
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vol. 107
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issue 5
864-867
EN
In the present contribution I focus on various effects affecting the slope of calculated electron-positron momentum densities for electrons from individual core shells. In particular, I discuss the influence of positron distribution, of approximation used for the electron-positron correlation functions, as well as of finite apparatus resolution on the resulting spectra.
3
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Influence of Atomic Sphere Radii on the Electron-Positron Momentum Density Calculated for SiC within the LMTO-ASA

100%
Rubaszek A.
Acta Physica Polonica A
|
2006
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vol. 110
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issue 5
683-689
EN
The atomic sphere approximation consists in replacing the Wigner-Seitz polyhedron, containing individual atom, by the sphere of the same volume. In the case of several not equivalent atoms per primitive cell, e.g. for SiC, the radii of atomic spheres, centred at different atoms, are not uniquely determined and should be judiciously chosen. In the present work one studies the effect of choice of atomic sphere radii on the resulting electron band structure and momentum density as well as the electron-positron momentum density. Calculations were performed for SiC within the linear muffin-tin orbital atomic sphere approximation method.
4
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Positron Annihilation Study of Defects in the Cage-Type Uranium Compound

100%
Rubaszek A.
|
|
vol. 125
|
issue 3
737-740
EN
The electron and positron properties of the UIr_2Zn_{20} compound of the Fd-3m cage-type crystal structure are studied. The characteristics for the perfect crystal are compared with their counterparts in the elements containing Ir and Zn vacancy. The presence of the vacancy hardly influences the electron charge density around individual atoms. In contrast to electrons, the positron is strongly localized inside the vacancy and the transfer of positron charge is observed. The positron lifetime, τ, appears to be strongly sensitive to the presence and type of the vacancy. Furthermore, this parameter calculated for the perfect crystal is very close to the experimental value for Zn. Here the theoretical values of τ depend on the approach applied to the electron positron (e-p) correlations.
5
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Densities of Valence Electrons in Simple Metals Effective with Respect to Electron-Positron Correlations

63%
Kontrym-Sznajd G., Rubaszek A.
Acta Physica Polonica A
|
1993
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vol. 83
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issue 3
333-337
EN
The influence of the electron-positron interactions on the momentum density of annihilation quanta in real metals is discussed. The role of momentum dependence of two-particle electron-positron correlations is set forth. The effective densities describing electron-positron correlations are presented for valence electrons in simple metals.
6
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Methods of Extracting Electron-Positron Enhancement Factors from Experimental ACAR Data

63%
Kontrym-Sznajd G., Rubaszek A.
Acta Physica Polonica A
|
1993
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vol. 83
|
issue 3
339-344
EN
Methods of extracting the full shape of the electron-positron momentum density from experimental angular correlation of positron annihilation radiation curves are discussed. The proposed analysis of experimental data allows more reliable verification of the form of electron-positron enhancement factors near the Fermi surface in simple metals.
7
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Electron-Positron Correlations in Paramagnetic Chromium

51%
Rubaszek A., Szotek Z., Temmerman W.
Acta Physica Polonica A
|
2001
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vol. 99
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issue 3-4
473-477
EN
Several approximations for the electron-positron interaction are applied to study the electron-positron momentum densities of paramagnetic chromium. The non-local and state selective electron-positron correlation functions, evaluated within the weighted density approximation, are used to calculate various positron annihilation characteristics in this system. The weighted density approximation results are compared to the experimental data, and to the corresponding results of the independent particle model, local density approximation, and generalised gradient approximation. Also, the semi-empirical results are used in gaining more physical insight and deriving final conclusions of this work.
8
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Non-Local Electron-Positron Enhancement Factors in Solids

51%
Rubaszek A., Szotek Z., Temmerman W.
|
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vol. 95
|
issue 4
652-658
EN
Non-local electron-positron correlation effects in solids are studied. The weighted density approximation is applied to calculations of the non-local electron-positron correlation functions. The calculated weighted density approximation electron-positron enhancement factors for the core electrons are compared with those obtained within the local density approximation. Also, differences in the electron-positron enhancement factors due to the s, p, d and f angular momentum channels of the electron charge density are studied. The formalism is applied to ab initio calculations of positron lifetimes in a variety of metals and silicon. The influence of various approximations to the electron-positron interaction on the positron lifetimes is also presented. The weighted density approximation results are compared to those calculated within the local density approximation, the recent generalized gradient approximation and with experimental data.
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