Electronic structure of linear chains of fullerenes V. A. Levashov, A. A. Remova, and V. R. Belosludov a) Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russia ~Submitted 25 March 1997! Pis’ma Zh. E ´ ksp. Teor. Fiz. 65, No. 8, 647–650 ~25 April 1997! The band structure of linear chains of fullerene molecules is calculated as a function of the intermolecular p -electron overlap integral T , which increases under increasing external pressure. Chains consisting of neu- tral (C 60 ) and charged (C 60 2 ) molecules are studied. It is shown that there is a sharp transition from a metal ~or narrow-gap semiconductor! to an insulator ~with band gap ;1 eV! with increasing T . The proposed model makes it possible to describe the formation of solid-carbon struc- tures, containing chains of covalently bound fullerene molecules, with different pressure-dependent semiconductor properties. © 1997 American Institute of Physics. @S0021-3640~97!01608-3# PACS numbers: 61.48.1c, 71.20.Tx Linear chains of fullerenes were recently discovered in A 1 C 60 compounds ~A 5 K, Rb, Cs, Na 2 Cs, Na 2 Rb!. 1–6 Phase transitions with a change of lattice symmetry are observed in these structures. In the orthorhombic phase the distance between the centers of the molecules in the direction of the crystallographic vector a equals only 9.1–9.3 Å. It is conjectured that the fullerene molecules form in this direction a polya- nion chain with covalently bound C 60 2 molecules. It is believed that the polymer bond in polyanion A 1 C 60 chains forms if the midpoint of the two closest parallel double bonds belonging to neighboring molecules falls on the intermolecular axis; the p electron orbitals of the two closest pairs of carbon atoms form an intermolecular overlap. The observation of identically oriented linearly polymerized neutral C 60 molecules in the solid phase was recently reported. Such chains are formed in amorphous fullerite structures at high pressures and temperatures. 7–10 The details of the mechanism of formation of the polymer chains have not been adequately studied. It is well known that the rigid-band model describes poorly the electronic structure of compounds of the type A x C 60 ( x 51, 2, 3, 4), where A is an alkali-metal atom. One reason for this could be the electron–phonon interaction. The band structure of fullerides reflects primarily the molecular structure of the highly symmetric C 60 . Since the three- fold degenerate t 1 u level forms the conduction band of A x C 60 compounds, the Jahn– Teller effect should play a fundamental role here. 11 The calculations were performed in a model proposed by Su, Schrieffer, and Heeger ~SSH!, 12 in which hops of the p electrons between neighboring carbon atoms are studied and the local electron–phonon interaction is treated in an adiabatic approximation. This approach was used in Ref. 13 to calculate the spectrum of an isolated fullerene molecule, and it was also shown that the formation of ‘‘long’’ and ‘‘short’’ bonds between the 683 683 0021-3640/97/080683-04$10.00 © 1997 American Institute of Physics