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Correlation and pairing in C 60 2 n − ions. Superconductivity of alkali and alkaline earth compounds of C 60
Author(s) -
Larsson Sven,
Rodriguezmonge Lucia
Publication year - 1993
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560480859
Subject(s) - pairing , chemistry , ion , superconductivity , alkali metal , ground state , electron pair , ionic bonding , electron , atomic physics , valence (chemistry) , atomic orbital , electronic correlation , alkaline earth metal , condensed matter physics , chemical physics , physics , molecule , organic chemistry , quantum mechanics
Hopping conductivity becomes activationless (metallic) when twice the intersite coupling supercedes the reorganization energy. Consistent with this idea, activationless electron pair transfer may be considered as a condition for the appearance of superconductivity. For electron pairs the condition is slightly more complicated than for single electrons. The activation energy depends on the relative energies between ionic states and a valence bond state. The latter serves as an intermediate state, contributing to the disappearance of the activation barrier. In A 3 C 60 , that pairing occurs because the 1 A g state of the negative ions C 60 2−and C 60 4−is stabilized by correlation effects and is the ground state. The correlation effects are primarily due to the closeness in energy and different parity of the t l u and t l g orbitals, which are partly occupied in the negative ions, but empty in neutral C 60 . The small interelectronic repulsion and the polarization energy from the environment also contribute to the stability of the evenly negative ions. © 1993 John Wiley & Sons, Inc.