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Role of relaxation and time-dependent formation of x-ray spectra
KTH, Superseded Departments, Biotechnology.
KTH, Superseded Departments, Biotechnology.
KTH, Superseded Departments, Biotechnology.ORCID iD: 0000-0002-1763-9383
2001 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 64, no 16Article in journal (Refereed) Published
Abstract [en]

A fundamental problem of x-ray spectroscopy is the role of relaxation of the electronic subsystem in the field of the transient core hole. The main intention of the present study is to explore the dynamics due to core-hole relaxation in the whole time domain, and to find out how it is manifested in finite molecular systems in comparison with solids. A technique is developed based on a reduction of the Nozieres-De Dominicis equation to a set of linear algebraic equations. The developed time-dependent formalism is applied to a numerical investigation of a one-dimensional tight-binding model. The formation of the x-ray profiles is explored on the real time scale, and the role of interaction with the core hole, band filling, and the final-state rule are investigated for systems of different size. The fort-nation of spectra of the infinite translational invariant system is studied by extensions of the finite systems. We found that the dynamics of finite systems, like molecules, differs qualitatively from solids: Contrary to the latter the time lapse of the Nozieres-De Dominicis domain for finite systems is squeezed between the inverse bandwidth and the revival time, which is proportional to the system size. For small molecules this means that there is no time for a "Mahan-Nozieres-De Dominicis singularity" to develop. Comparison with the strict solution of the Nozieres-De Dominicis equation shows that the adiabatic approximation describes x-ray absorption and emission considerably better than the fast approximation. This explains the suppression of the relaxation effects in x-ray emission of, e.g., gas phase and surface adsorbed molecules, but also that these effects are essential for the absorption case. There is still a quantitative distinction between the adiabatic approximation and the strict approach, which becomes more important for larger systems. Adopting the so-called finite state rule by von Barth and Grossman also for molecules, an almost complete numerical agreement between this rule and the strict x-ray-absorption and emission profiles for systems of different sizes is obtained. The simulations indicate that the final-state rule correction is important mainly near the absorption edge and at the top of the emission band.

Place, publisher, year, edition, pages
2001. Vol. 64, no 16
Keyword [en]
extra-atomic relaxation, narrow-band metals, edge problem, adsorbates
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-13774DOI: 10.1103/PhysRevB.64.165115ISI: 000171866400036OAI: oai:DiVA.org:kth-13774DiVA: diva2:327365
Note
QC 20100629Available from: 2010-06-29 Created: 2010-06-28 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Electronic and nuclear dynamics of X-ray processes
Open this publication in new window or tab >>Electronic and nuclear dynamics of X-ray processes
2001 (English)Doctoral thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2001. viii, 68 p.
Keyword
resonant X-ray Raman scattering, nuclear dynamics, relaxation
National Category
Industrial Biotechnology
Identifiers
urn:nbn:se:kth:diva-3189 (URN)91-7283-095-6 (ISBN)
Public defence
2001-06-12, 00:00
Note
QC 20100628Available from: 2001-06-08 Created: 2001-06-08 Last updated: 2010-06-29Bibliographically approved

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Ågren, Hans

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