Naoya Iwahara

Dynamical Jahn-Teller effect and antiferromagnetism in Cs3C60.

The dynamical Jahn-Teller effect on fullerene sites in insulating Cs(3)C(60) is investigated fully ab initio. The vibronic excitations of rotational type are at ≥ 65 cm(-1), while the net kinetic contribution to the Jahn-Teller stabilization energy constitutes approximately 90 meV. This means that no localization of distortions by intermolecular interactions is possible in these fullerides; therefore, free rotations of deformations take place independently on each C(60). The latter destroy the orbital ordering and establish a conventional exchange interaction between S = 1/2 on fullerene sites. The corresponding exchange model is derived and predicts the Néel temperature for A15 Cs(3)C(60) close to experiment.

Giant exchange interaction in mixed lanthanides

Combining strong magnetic anisotropy with strong exchange interaction is a long standing goal in the design of quantum magnets. The lanthanide complexes, while exhibiting a very strong ionic anisotropy, usually display a weak exchange coupling, amounting to only a few wavenumbers. Recently, an isostructural series of mixed (Ln = Gd, Tb, Dy, Ho, Er) have been reported, in which the exchange splitting is estimated to reach hundreds wavenumbers. The microscopic mechanism governing the unusual exchange interaction in these compounds is revealed here by combining detailed modeling with density-functional theory and ab initio calculations. We find it to be basically kinetic and highly complex, involving non-negligible contributions up to seventh power of total angular momentum of each lanthanide site. The performed analysis also elucidates the origin of magnetization blocking in these compounds. Contrary to general expectations the latter is not always favored by strong exchange interaction.

Critical reinvestigation of vibronic couplings in picene from view of vibronic coupling density analysis

Vibronic coupling constants in the monoanionic, trianionic, and excited states of picene are evaluated from the total energy gradients using the density functional theory. Employing the calculated vibronic coupling constants in the excited state of the neutral molecule, electron energy loss spectrum (EELS) is simulated to be compared with the experimental spectrum. The calculated vibronic coupling constants are analyzed in terms of the vibronic coupling density which enables us to analyze vibronic couplings based on the relation between the electronic and vibrational structures. The vibronic coupling constants reported by Kato et al. [J. Chem. Phys. 116, 3420 (2002) and Phys. Rev. Lett. 107, 077001 (2011)] are critically discussed based on the vibronic coupling density analysis.

Vibronic Coupling Constant and Vibronic Coupling Density

The Jahn–Teller effect [7–9, 25] originates from vibronic coupling [19]. In this chapter, we discuss the definition of vibronic coupling with emphasis on its difference from non-adiabatic coupling. We present one of the methods for calculation of the vibronic coupling constant and vibronic coupling density analysis that enables us to investigate the local properties of vibronic coupling. Some applications of vibronic coupling density are presented. Vibronic couplings in fullerene ions still contain some unresolved problems as targets for the calculations. Studies on vibronic couplings in fullerene ions are reviewed.

Dynamical Jahn-Teller instability in metallic fullerides

Dynamical Jahn-Teller effect has escaped so far direct observation in metallic systems. It is particularly believed to be quenched also in correlated conductors with orbitally degenerate sites such as cubic fullerides. Here the Gutzwiller approach is extended to treat electron correlation over metals with Jahn-Teller active sites and applied to the investigation of the ground state of K

Orbital disproportionation of electronic density is a universal feature of alkali-doped fullerides

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Vibronic coupling density and related concepts

C

Effect of Coulomb interactions on the vibronic couplings in C60(

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Zeeman interaction and Jahn-Teller effect in the Γ8 multiplet

. It is shown that dynamical Jahn-Teller instability fully develops in this material when the interelectron repulsion

New mechanism of kinetic exchange interaction induced by strong magnetic anisotropy

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