Ab initio electronic structure of the eclipsed and staggered conformations of the kappa-(BEDT-TTF)(2)Cu[N(CN)(2)] Br organic superconductor

Abstract

We investigated ab initio the electronic structure of both conformers exhibited by the kappa-(BEDT-TTF)(2)Cu[N(CN)(2)] Br organic superconductor at ambient as well as low temperatures. We found that the eclipsed structure is approximatively 0.35 eV/formula more stable than the staggered one. We found that two energy barriers separate both structures: one consistent with the experimental values close to 2000-2600 K. A second energy barrier, for the reversed process and close to 20 K, could explain the ethylene group freezing found at low temperatures.