Polarons in linear chains of fullerenes V. A. Levashov, A. A. Remova, and V. R. Belosludov a) Institute of Inorganic Chemistry, 630090 Novosibirsk, Russia ~Submitted 6 September 1996! Pis’ma Zh. E ´ ksp. Teor. Fiz. 64, No. 8, 521–525 ~25 October 1996! Polaron states in linear chains of fullerenes are studied with the use of the generalized model of Su–Shrieffer–Heeger ~SSH! for the intermo- lecular and intramolecular degrees of freedom. Electron charge distri- butions over the molecular surface and Jahn–Teller distortions of car- bon atoms in C 60 are calculated self-consistently for linear C 60 polymer and C 60 2 polyanion chains. A polaron band narrowing is examined. It is shown that the polymerization of C 60 molecules in phase transitions may be caused by the cooperative Jahn–Teller effect. © 1996 Ameri- can Institute of Physics. @S0021-3640~96!00220-4# PACS numbers: 75.10.Jm, 75.30.Ds Recently a number of structural and electronic phase transitions have been found in fullerides. In particular, the existence of a phase consisting of linear polymer chains in A 1 C 60 compounds ~A5K, Rb, Cs, Na 2 Cs, Na 2 Rb! has come into focus. 1–6 The low temperature structure of A 1 C 60 is orthorhombic with an unusually short separation of 9.1–9.3 Å between the centers of C 60 molecules along one of the crystallographic direc- tions. It has been suggested that the anions in the orthorhombic phase of these com- pounds are linear chains of covalently bonded C 60 molecules. Moreover, the amorphiza- tion of C 60 under pressure has become a hot issue in high-pressure science and materials science. 7,8 Amorphous-carbon structures based on linear-polymerized C 60 molecules have been found at pressures above 5 GPa. 9 The details of the reaction mechanism for the C 60 and C 60 2 chain formation are as yet unclear. 10–12 It is well known that the Jahn–Teller effect leads to a dynamic instability of sym- metrical configurations of molecules. In crystal structures this effect can possibly become static. The band structure of alkali-doped fullerides reflects primarily the molecular or- bitals of high-symmetry C 60 . It is now well established that the threefold degenerate t 1 u lowest unoccupied state of C 60 is the conduction band of A x C 60 compounds. In our previous work 9 we studied the band reconstruction of K x C 60 ~x 51,2,3,4! crystals caused by the cooperative Jahn–Teller effect. A simple model was proposed there to describe non-rigid-band effects in alkali-doped fullerides. The band structures of solid K x C 60 ~x 51,2,3,4! and the cooperative Jahn–Teller distortions of C 60 molecules were calculated self-consistently. The band calculations were performed in the frame- work of the SSH model. The model takes into account the p-electron hopping between carbon atoms and local electron–phonon interactions and employs the adiabatic approxi- mation. The SSH model has been extended to the case of doped fulleride crystals: 9 besides the intramolecular electron transfer, we introduced there the p-electron hopping 567 567 0021-3640/96/080567-06$10.00 © 1996 American Institute of Physics