Localization of Electrons in Extended Systems

Larsson, Sven; Klimkñs, Agris

doi:10.1080/10587250108023662

Cited by 18 publications

(11 citation statements)

References 34 publications

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“…Since the theoretical treatment starts from a local treatment, it has been possible to use total energy potential surfaces. Non-observables or irrelevant observables ('Mott-Hubbard U') were avoided in the definition of a reasonable delocalisation concept [16]. The concepts used are standard in modern theoretical chemistry but are surprisingly neglected among theoretical solid-state physicists.…”

Section: Discussionmentioning

confidence: 99%

“…The conductivity is increased by several orders of magnitude at high pressures of a few GPa [30][31][32][33], but superconductivity has not been reported. High pressure leads to decreased activation barrier (see below) and at the same time to an insulator to metal transition, of obvious relevance also to superconductivity [3,16]. Well's salt, CsAuCl 3 , is probably the first and best-known example of disproportionation in gold compounds [29][30][31][32][33].…”

Section: +mentioning

confidence: 99%

“…same result, of course. The mentioned deloncept may be extended to infinite systems [16]. ameters are needed to decide whether the syszed or delocalised: reorganization energy (λ) coupling (∆/2).…”

Section: Theorymentioning

confidence: 99%

“…A quantum chemical calculation of wave function and geometry gives the same result, of course. The mentioned delocalisation concept may be extended to infinite systems [16]. Only two parameters are needed to decide whether the system is localized or delocalised: reorganization energy (λ) and effective coupling (∆/2).…”

Section: Introductionmentioning

confidence: 99%

“…Unfortunately the latter fact has lead to some confusion on the connection between superconducting and MV systems. A theory for electronic localization has been set up [14][15][16] on the basis of coupling between electronic and nuclear motion. In this theory reorganization energy λ 'competes' with coupling energy ∆.…”

Section: Introductionmentioning

confidence: 99%

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Mixed valence model for superconductivity

Larsson¹

2003

Braz. J. Phys.

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Superconductivity often occurs in crystals with one active electron per site with charge density wave (CDW) or spin density wave (SDW) as 'mother state'. It is proposed that superconductivity is possible when the differences in equilibrium geometry and energy between the diabatic CDW and SDW states are so small that there is interaction between them via the zero point vibrations. Electron pairing in real space is directly related to oxidation states being different in two units. Three valence states in succession have to be stable (ground state or low-energy excited states) and we therefore refer to this mixed valence model as the MV-3 model. Examples are chosen from bismuthates, cuprates, and fullerides. The theory is simple and straightforward and offers solutions to other important problems as well, for example for A 3 C 60 (A = K, Rb), that (1) there are no magnetic moments in crystal phase, and (2) that these systems are superconducting metals while A 4 C 60 are insulators.

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Section: Discussionmentioning

confidence: 99%

Section: +mentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mixed valence model for superconductivity

Larsson¹

2003

Braz. J. Phys.

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Superconductivity in Copper, Silver, and Gold Compounds

Larsson

2004

Chemistry A European J

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High-temperature superconductivity exists in layered, square-planar cuprates, but is almost absent in most other Cu(II) compounds and in most Ag(II) and Au(II) compounds. Valence state II is quite unusual in silver and gold and often disproportionates to valence states I and III ("negative-U compounds"). The two-electron difference in oxidation state is suggestive of electron pairing, a prerequisite for superconductivity. In the present paper the connection between disproportionation and geometrical structure on one hand and superconductivity on the other is discussed by using the accepted theory for mixed valence complexes. It is concluded that absence of superconductivity in gold and silver compounds can be connected to the instability of oxidation state II and the large difference in equilibrium geometry between oxidation states I and III.

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Chemical model for superconductivity

Larsson

2002

Int J of Quantum Chemistry

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ABSTRACT:A "chemical" model based on the theory of mixed valence systems is successful in explaining a number of properties of superconductors. The model is formulated in configuration space but is consistent with Bardeen-Cooper-Schrieffer theory, and connects directly to chemical properties that may be calculated by quantum chemical methods. Crystal structure is important, in particular the difference in equilibrium geometry between different oxidation states. According to the model, high pressure causes less difference between the oxidation states and hence a lower, or possibly disappearing, activation barrier and increased conductivity. This agrees with the experiments. Mixed valence systems with nonequivalent sites or with a large structural difference between the oxidation states are not superconducting or even conducting.

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Localization of Electrons in Extended Systems

Cited by 18 publications

References 34 publications

Mixed valence model for superconductivity

Mixed valence model for superconductivity

Superconductivity in Copper, Silver, and Gold Compounds

Chemical model for superconductivity

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