Quantum Chemistry in Moldova – 50 Years

An overview of the main achievements of the Laboratory of Quantum Chemistry of the Institute of Chemistry of the Academy of Sciences of Moldova during the 50 year of its existence is briefly outlined. The main fundamental non-transient result obtained in this laboratory is the generalization of the Jahn-Teller effect theory formulated and proved as a general law of instability of polyatomic systems and its application to a variety of physical, chemical, and biological problems, including al-range spectroscopy, geometry and spectra of molecular systems, structural phase transitions, ferroelectricity, stereochemistry and crystal chemistry, chemical activation and reactivity, electron transfer in mixed-valence compounds, and electron-conformational transitions in biological systems.

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Manganites

Superconducting State ◽

10.1093/oso/9780198845331.003.0009 ◽

2021 ◽

pp. 403-428

Author(s):

Vladimir Z. Kresin ◽

Sergei G. Ovchinnikov ◽

Stuart A. Wolf

Keyword(s):

Colossal Magnetoresistance ◽

Mixed Valence ◽

Fundamental Property ◽

Microscopic Theory ◽

Double Exchange ◽

Metallic State ◽

Electron Hole ◽

Jahn Teller ◽

Jahn Teller Effect ◽

Mixed Valence Compounds

This chapter focuses on manganites. There is a large similarity between the two families of mixed-valence compounds, the cuprates and the manganites. However, manganites display colossal magnetoresistance. The most fundamental property of manganites is the strong correlation between their transport properties and their magnetic properties. This correlation is caused by the double-exchange mechanism. The Hund interaction and the Jahn–Teller effect are the key ingredients of the microscopic theory. The transition to the ferromagnetic and metallic state is of a percolative nature. The superconducting–antiferromagnetic–superconducting Josephson junction is described. One can observe giant oscillations of the Josephson current as a function of a weak external magnetic field. The main properties, including the electron–hole asymmetry can be described in the framework of a generalised two-band picture. A peculiar isotope effect can be observed.

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Cooperative Pseudo Jahn-Teller Effect as Microscopic Mechanism of (OMT)-(LTT) Structural Phase Transition in La2−xBaxCuO4Superconductors

MRS Proceedings ◽

10.1557/proc-291-223 ◽

1992 ◽

Vol 291 ◽

Cited By ~ 1

Author(s):

Michael D. Kaplan

Keyword(s):

Phase Transition ◽

Structural Phase Transition ◽

Structural Phase ◽

Electronic States ◽

Teller Effect ◽

Excited Electronic States ◽

Microscopic Mechanism ◽

Jahn Teller ◽

Jahn Teller Effect ◽

Local Distortions

ABSTRACTA microscopic mechanism for the structural phase transition from the orthorhombic mediate temperature (OMT) phase into the low temperature tetragonal (LTT) one is suggested on the basis of the cooperative pseudo Jahn-Teller effect. The local distortions mixing the ground and the first excited electronic states are ordered antiferrodistortively and are connected in part, with the oxygen octahedra rotations around the [100] axis. The results are in agreement, with the neutron scattering experiments data.

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