Orientational Order in A3C60: Effects on Valence Bands and Infrared Optical Spectra
By analysis of the electronic contribution to the binding in A3C60, we show that the problem of orientational ordering can be mapped onto the fcc nearest-neighbor antiferromagnetic Ising model with J of the order of 100K. The ground state crystal structure should be therefore anti-ferromagnetically ordered in two dimensions and disordered in the third. This is not inconsistent with present X-ray powder data. We find that the low-temperature conduction-band structure closely resembles that of the simplest antiferromagnetically ordered (so-called bi-directional) crystal. Calculated optical conductivity can be fitted by a Drude-like contribution and an “interband” Lorenzian peak at 400-500 cm−1.
KeywordsEntropy Fullerene Erwin CuAu
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- The TB rad-AO results of the present paper were obtained with a=14.24 Åand bond lengths 1.391Å and 1.455Å.. The results were corrected for the structural difference in the repulsive interaction, which is assumed to be atomic and of form A/R 12, where R is the inter-atomic distance. A was adjusted so that the correct lattice parameter was obtained for C60 in the presence of a van der Waals interaction (∝ d −6, where d is the separation between two molecules) of —1.7 eV at equilibrium.Google Scholar
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