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Exchange Contributions to Spin Polarization in Low-Energy Electron Scattering from Xe and Hg

100%
Sienkiewicz J. E., Fritzsche S., Syty P.
Acta Physica Polonica A
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2000
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vol. 98
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issue 1-2
41-46
EN
The contribution of exchange interactions is investigated for spin polarization of electrons which are scattered elastically from xenon and mercury at the energy of 1.5 eV. We find that electron exchange between the bound-state and the scattered electron gives rise to a substantial spin polarization in both cases.
2
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Two-Component Relativistic Hamiltonians and the Douglas-Kroll Approximation

100%
Barysz M.
Acta Physica Polonica A
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2002
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vol. 101
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issue 6
815-823
EN
The iterative solutions of the previously derived operator equation which defines an open-ended formalism for the reduction of the 4-component Dirac Hamiltonian to 2-component "electronic" operators of arbitrarily high accuracy, are discussed. It is shown that by departing from the approach based solely on the operator algebra one can define the initial iterative solution which leads to the 2-component Douglas-Kroll Hamiltonian. The present derivation reveals the origin of the success of methods based on the Douglas-Kroll Hamiltonian. It also shows that among relatively simple 2-component Hamiltonians, which are exact through the fourth power of the fine structure constant, the Douglas-Kroll operator is the most complete one. Also a computationally convenient and highly compact formula for matrix elements of the Douglas-Kroll Hamiltonian is obtained as a by-product of this investigation.
3
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A Comparison of Different Approximate Two-Component Relativistic Theories of Many-Electron Systems: A Case Study of the Ionization Energies of Two-Electron Ions

100%
Barysz M., Flocke N., Karwowski J.
Acta Physica Polonica A
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2001
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vol. 99
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issue 6
631-641
EN
The corrections to the ionization energies of two-electron ions due to relativistic effects are studied by different two-component relativistic methods. In particular, the results obtained by the standard Pauli-Cowan-Griffin method and by two variants of the Douglas-Kroll-Hess method (the one based on the free-particle transformation and the one in which the transformation accounts for the nuclear potential) are compared with those calculated using the four-component Dirac-Fock method. Limits of applicability of each of these methods have been indicated. Results acceptable in the whole range of the nuclear charge (relativistic corrections accurate up to 4% for Z≤85) are given only by the Douglas-Kroll-Hess method which goes beyond the free-particle transformation. Each of the other two approaches either underestimates or overestimates the corrections due to relativistic effects.
4
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On the Accuracy of the Discretization Techniques in Approximate Relativistic Methods

100%
Woźniak D., Sadlej A. J.
Acta Physica Polonica A
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2000
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vol. 98
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issue 6
673-690
EN
Several non-singular 2-component methods for relativistic calculations of the electronic structure of atoms and molecules lead to cumbersome operators which are partly defined in the coordinate representation and partly in the momentum representation. The replacement of the Fourier transform technique by the approximate resolution of identity in the basis set of approximate eigenvectors of the p^{2} operator is investigated in terms of the possible inaccuracies involved in this method. The dependence of the accuracy of the evaluated matrix elements on the composition of the subspace of these eigenvectors is studied. Although the method by itself appears to be quite demanding with respect to the faithfulness of the representation of the p^{2} operator, its performance in the context of the standard Gaussian basis sets is found to be encouragingly accurate. This feature is interpreted in terms of approximately even-tempered structure of the majority of Gaussian basis sets used in atomic and molecular calculations.
5
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Towards relativistic ECP / DFT description of chemical bonding in E112 compounds: spin-orbit and correlation effects in E112X versus HgX (X=H, Au)

51%
Zaitsevskii A., Rykova E., Mosyagin N., Titov A.
Open Physics
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2006
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vol. 4
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issue 4
448-460
EN
The relativistic effective core potential (RECP) approach combined with the spin-orbit DFT electron correlation treatment was applied to the study of the bonding of eka-mercury (E112) and mercury with hydrogen and gold atoms. Highly accurate small-core shape-consistent RECPs derived from Hartree-Fock-Dirac-Breit atomic calculations with Fermi nuclear model were employed. The accuracy of the DFT correlation treatment was checked by comparing the results in the scalar-relativistic (spin-orbit-free) limit with those of high level scalar-relativistic correlation calculations within the same RECP model. E112H was predicted to be slightly more stable than its lighter homologue (HgH). The E112-Au bond energy is expected to be ca. 25–30 % weaker than that of Hg-Au. The role of correlations and magnetic (spin-dependent) interactions in E112-X and Hg-X (X=H, Au) bonding is discussed. The present computational procedure can be readily applied to much larger systems and seems to be a promising tool for simulating E112 adsorption on metal surfaces.
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