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Abstract

Electron-intramolecular-phonon coupling and its role in the
occurrence of possible superconductivity in the monoanions of
coronene (C24H12) and corannulene (C20H10) are studied.
Electron-intramolecular-phonon coupling constants are
calculated from the intramolecular vibronic coupling constants.
The C-C stretching E-2g mode of 1668 cm(-1) plays an essential
role in the electron-intramolecular-phonon coupling in the
monoanion of coronene while the low frequency E-2 modes, which
have a radial character, and the C-C stretching mode of 1669
cm(-1), which has a tangential character, afford large
electron-intramolecular-phonon coupling constants in the
monoanion of corannulene. The calculated total electron-
intramolecular-phonon coupling constant for the monoanion of
corannulene (0.269 eV) is much larger than that for coronene
monoanion (0.076 eV). The intermediate characteristics between
sigma and pi orbital interaction properties owing to the bowl-
shaped structure of corannulene make orbital interactions
between two neighboring carbon atoms strong, and thus electron-
intramolecular-phonon coupling is stronger in the monoanion of
corannulene than that in the monoanion of coronene. Possible
superconducting transition temperature T-c value for the
monoanion of corannulene is estimated to be an order of
magnitude larger than that for the monoanion of coronene; for
example, the calculated values of T(c)s for the monoanions of
coronene and corannulene are about 0.05-8.86 and 29.17-65.56 K,
respectively, in the range of n(0)=4-5 and mu*=0.10-0.20, where
n(0) is the density of states at the Fermi level (states per
eV, per spin, and per molecule) and mu* is the Coulomb
pseudopotential. The relationships between structures and T(c)s
in alkali-doped A(3)C(60) complexes and graphite intercalation
compounds (GICs) are also discussed from a viewpoint that
corannulene can be viewed as a fragment of C-60 and coronene as
a fragment of one-sheet graphite. (C) 2002 American Institute
of Physics.