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Charge Carrier's Deformability: Carrier‐Induced Vibrational Softening
Author(s) -
Emin D.
Publication year - 2000
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/(sici)1521-3951(200003)218:1<259::aid-pssb259>3.0.co;2-c
Subject(s) - charge carrier , bipolaron , intermolecular force , chemical physics , molecular physics , softening , materials science , singlet state , chemistry , condensed matter physics , molecule , atomic physics , polaron , electron , physics , optoelectronics , excited state , organic chemistry , composite material , quantum mechanics
The wave functions of charge carriers deform in response to their interactions with a solid's atoms and with other carriers. The free energy of a charge carrier confined to a molecule embedded in a polar medium is expressed as a function of the carrier's spatial extent. A localized carrier assumes the configuration that minimizes its free energy. An intermolecular hop requires passing through a coincidence configuration in which a carrier is shared between equivalent molecules. Rates for intermolecular jump processes are described in terms of the spatial extents of static and coincident carriers. Bipolaron formation depends on the carriers' interactions with each other as well as with surrounding atoms. When the two carriers occupy degenerate orbitals, symmetry‐breaking atomic deformations are required to stabilize a singlet with respect to a triplet. The energies of these atomic deformations are lowered by the carriers adjusting to them. The reduction of the vibrational free energy arising from singlet‐induced softening can stabilize the singlet. Distinctive properties of boron carbides' bipolarons suggest that they are “softening bipolarons.”