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- Almbladh, Carl-Olof, et al.
(author)
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BANDSTRUCTURE AND LOCALIZED DESCRIPTIONS OF NARROW-BAND SYSTEMS
- 1988
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In: Narrow-Band Phenomena—Influence of Electrons with Both Band and Localized Character. ; 184, s. 81-89
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Book chapter (peer-reviewed)abstract
- In this note I would like to give some personal views on the relevance of bandstructure treatments of narrow-band systems. At first sight one might think that bandstructure theory is not a very appropriate framework for quasi-localized electrons. Nevertheless, it has been found that density-functional (DF) theory in its modern form gives a rather impressive description of ground-state properties for the majority of systems, not only " in principle " but also in practice via calculations based on the local-density approximation (LDA). I will here discuss some key concepts in DF theory with emphasis on physical significance of the eigenvalues which appear in the DF one-electron-like equations. I will also to some extent discuss the dynamical selfenergy Σ, which describes the " one-electron " excitations reached by adding or removing an electron, although there is very little work done for narrow-band electrons.
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- Almbladh, Carl-Olof, et al.
(author)
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Density-Functional Theory and Excitation Energies
- 1985
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In: Density Functional Methods in Physics. - 9781475708189 - 9781475708202 ; , s. 209-231
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Book chapter (peer-reviewed)abstract
- During the past decade, the local-density (LD) approximation within density-functional (DF) theory has been the most important method for obtaining the electronic properties of realistic systems. The limitations of the method have to a large extent been computational in nature rather than theoretical. The conceptually simple one-particle equations arising in the method have often been too difficult to solve in systems with low symmetry such as amorphous systems or surfaces. However, due to our increased understanding of these systems the computational techniques are quickly developing, and we forsee an even greater importance of the method in the near future. The theoretical limitations of the method will then become more evident and result in an urgent need for improvements beyond the LD approximation. Such a need exists already today in many systems such as, e.g., atoms and molecules. The description of correlation effects in these systems is necessary and important and the answers provided by the LD approximations are often too poor to be of practical use. Unfortunately, for a long time, only minor theoretical advances were made since the modern version of DF theory was laid down by Hohenberg, Kohn, and Sham1,2 in the mid sixties.
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- Almbladh, Carl-Olof, et al.
(author)
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Many-Body Theory of Auger Processes in Metals and Semiconductors
- 1988
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In: Recent Progress in Many-Body Theories. - 9781461309734 ; 1, s. 317-328
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Book chapter (peer-reviewed)abstract
- Auger spectra of solids arise from radiationless decay of innershell vacancies created by x-ray or electron bombardment. In a corevalence-valence (CVV) Auger process, for instance, one valence electron is filling the core hole while another valence electron is ejected and carries away the excess energy. The core hole is essentially dispersionless, and thus the spectrum of emitted electrons would, in the simplest one-electron picture, reflect the self-folded valence-electron state density. Such a simple model is, of course, grossly oversimplified, and the importance of matrix element effects has been demonstrated by several authors.1 However, no detailed investigation of many-body effects has been presented thus far for sp-bonded materials, and the current view is that one electron theory and bulk wavefunctions suffice to explain the experimental results.
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- Andersson, Greger, et al.
(author)
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Mässingsmusik - folkets bildning och nöje
- 1981
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In: Från forna tiders mässingssextett till våra dagars Symphonic Band. ; , s. 4-6
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Book chapter (pop. science, debate, etc.)
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