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    Wyświetlanie 1-9 z 9
    Tytuł:
    Influence of Many-Body Effects in Real Metals on Electron-Positron Momentum Distributions
    Autorzy:
    Boroński, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/1196046.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    71.18.+y
    71.60.+z
    71.15.Mb
    71.10.Ca
    Opis:
    It is shown that if one takes into account the effective mass of the electron, which in real structures is actually different than the free electron mass, the electron and positron self-energy effects may result in flatter and smaller enhancement of the electron-positron momentum distribution. Thus, the many-body effects mentioned above, among other reasons like e.g. influence of lattice potential on electron and positron wave functions, can be responsible for decreasing of the discontinuity on the Fermi momentum and a greater smearing of the Fermi surface seen in several angular correlation of positron annihilation radiation experiments.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 706-709
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Investigation of Electron-Positron Correlations by Monte Carlo Simulation
    Autorzy:
    Boroński, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/2042170.pdf
    Data publikacji:
    2005-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    78.70.Bj
    02.70.Ss
    Opis:
    Earlier theoretical studies, as well as recent calculations of positron annihilation rates in metals, show that some basic problems concerning electron-positron (e-p) interaction have not been solved satisfactorily, even for homogeneous media (the electron gas). In turn, the "computer experiments" e.g. quantum Monte Carlo simulations applied to these problems by several authors yielded only fragmentary, inaccurate and even incorrect results for smaller electron densities. It is shown in the present paper that the quantum Monte Carlo method may be useful in investigations of positron interactions with electrons. Reasonable annihilation rates have been obtained owing to appropriate construction of the trial function and taking into account the 3-particle correlations (i.e. dependence of the electron-electron (e-e) interaction on the distance from the positron). Moreover, the method of "exact determination" (without any fitting) of positron annihilation rates on the basis of the variational trial function was proposed. One also found the way of calculating the momentum dependent enhancement factors, the quantities not achievable within the Monte Carlo method until now.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 4; 576-585
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    A New Project for Calculations of e$\text{}^{+}$-e$\text{}^{-}$ Interaction in Real Metals
    Autorzy:
    Boroński, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/2007917.pdf
    Data publikacji:
    1999-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    71.10.-w
    71.60.+z
    Opis:
    A method based on numerical relaxation technique is proposed for solving directly the three-dimensional Euler-Lagrange equation for the density amplitude of conduction electrons in real metals disturbed by the positron. The method has been tested with good results for the positron in an inhomogeneous electron gas. The preliminary calculations of positron screening in lithium give hope for effective applications to real systems.
    Źródło:
    Acta Physica Polonica A; 1999, 95, 4; 461-468
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron-Positron Interaction in Metals. Theory and Experiment
    Autorzy:
    Stachowiak, H.
    Boroński, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/2042125.pdf
    Data publikacji:
    2005-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    78.70.Bj
    Opis:
    The electron-positron interaction greatly complicates the interpretation of positron annihilation data. The two-detector Doppler measurements of Mijnarends et al. as well as our theoretical calculations point at the conclusion that the local density approximation to e$\text{}^{+}$-e$\text{}^{-}$ interaction is a good way of treating this problem in real metals, at least the simplest ones. This shows that e$\text{}^{+}$-e$\text{}^{-}$ interaction in an electron gas is the key to understanding this phenomenon also in inhomogeneous systems. On the basis of dozens of experiments one comes to the conclusion that the well known formula of Boroński and Nieminen for the electron accumulation on the positron in jellium describes the best the positron lifetimes in metals. However, it is based on the calculations of Lantto which start from a physically oversimplified trial function. The results of Arponen and Pajanne, of Rubaszek and Stachowiak, and of Stachowiak and Lach lead to too short positron lifetimes in spite of using less controversial assumptions. The discrepancy is of the order of 8 to 15% for r$\text{}_{s}$=2. This shows that we still do not fully understand e$\text{}^{+}$-e$\text{}^{-}$ interaction even in an electron gas.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 4; 541-553
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron-Positron Interaction in Jellium: Optimization of the Perturbed Hypernetted-Chain Approach
    Autorzy:
    Stachowiak, H.
    Boroński, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047162.pdf
    Data publikacji:
    2006-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    78.70.Bj
    71.10.Ca
    Opis:
    The perturbed hypernetted-chain approach to electron-positron interaction in jellium consists in assuming the wave function of the system in the form of a Slater determinant built of single-electron functions presented asψi k(s)=w(s)φ$\text{}_{i}$ k(s). s is the distance between the electron and the positron. The function w(s) is obtained by solving the equation of Gondzik and Stachowiak. The functionφ$\text{}_{i k}$(s) is computed by applying a self-consistent Born approximation. The idea of the paper is to modify the function w(s) in such a way as to obtain from the Born approximation as precise results as possible. It is shown that the influence of such modifications on physical predictions is small. This shows how good is the perturbed hypernetted-chain approach. The annihilation rates obtained in such a way decrease somewhat, becoming closer to experimental expectations.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 5; 709-720
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron-Positron Interaction in Jellium: Modification of the Perturbed Hypernetted-Chain Approach
    Autorzy:
    Stachowiak, H.
    Boroński, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812551.pdf
    Data publikacji:
    2008-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    78.70.Bj
    Opis:
    The approach of Kahana to the electron-positron interaction in an electron gas contains the superfluous assumption that electron scattering on the positron can occur only to momentum states lying outside the Fermi sphere. The perturbed hypernetted-chain approach avoids that assumption, but self-consistency was achieved only in the Born approximation. In the present work a modification of perturbed hypernetted-chain approach allowed to reach self-consistency also at the Kohn-Sham level, at least for 1 ≤ r_s ≤ 3.5. The electron-positron correlation functions obtained in this way are compared to figures resulting from other approaches.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 5; 1523-1532
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electroni-Positron Scattering in Real Metals
    Autorzy:
    Boroński, E.
    Daniuk, S.
    Stachowiak, H.
    Powiązania:
    https://bibliotekanauki.pl/articles/1928926.pdf
    Data publikacji:
    1993-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    71.60.+z
    Opis:
    The purpose of the paper is to point at the importance of some detailed studies of electron-positron scattering in real metals using wave functions obtained from band structure calculations. In this work some preliminary investigations of the matrix elements of electron-positron scattering, e.g. the transitions from occupied to non-occupied states close to the Fermi surface are presented. One can observe that for s → s transitions of the positron (s, p are orbital quantum numbers) electrons do not change their orbital quantum numbers but for s → p transitions of the positron, electron quantum numbers change by unity.
    Źródło:
    Acta Physica Polonica A; 1993, 83, 3; 255-260
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Effective Electron-Positron Potential in Jellium
    Autorzy:
    Stachowiak, H.
    Boroński, E.
    Lach, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1929114.pdf
    Data publikacji:
    1993-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    71.60.+z
    Opis:
    One of the methods of determining theoretical annihilation characteristics in real metals is the approximation called Bloch modified ladder approach. In this approach a Bethe-Goldstone type equation is solved with an effective electron-positron potential obtained previously for jellium of the corresponding electron density. If one wishes to include the dependence on the local electron density of the e$\text{}^{+}$-e$\text{}^{-}$ effective potential in this formalism, it is necessary to know this potential for jellium, for metallic and above metallic densities. A review of different proposed e$\text{}^{+}$-e$\text{}^{-}$ potentials is presented and their correctness is evaluated from the point of view of their application in a Bethe-Goldstone type formalism which is the jellium analogue of Bloch modified ladder approach.
    Źródło:
    Acta Physica Polonica A; 1993, 83, 3; 391-394
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Enhancement Factors for Electrons in Solids for Some Simple Cases
    Autorzy:
    Stachowiak, H.
    Boroński, E.
    Banach, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/2025066.pdf
    Data publikacji:
    2001
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.60.+z
    78.70.Bj
    Opis:
    The approach to e$\text{}^{+}$-e$\text{}^{-}$ interaction in jellium proposed by Gondzik and Stachowiak proved to be simple numerically and leading to reasonable results. This is why it seemed to be particularly suited for generalizations to real solids, a problem that in spite of more than thirty years of research in this direction did not get yet a satisfactory solution. An obstacle up to now was the necessity to solve integro-differential equations in two dimensions. After overcoming this difficulty we were able to compute e$\text{}^{+}$-e$\text{}^{-}$ enhancement for core and valence electrons in lithium and for core electrons in other two-electron core elements. Properties of the electronic cloud screening the positron are investigated for different coordinates of this particle. The results are compared to such simplifying guesses concerning this problem as the local density, the generalized gradient and the weighted density approximations.
    Źródło:
    Acta Physica Polonica A; 2001, 99, 3-4; 503-513
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-9 z 9

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