Atomic and electronic structures of the high-pressure superconductor beta '-(BEDT-TTF)(2)ICl2: A first-principles study of the pressure effects

We predict theoretically the lattice parameters, internal coordinates, and electronic structures of the high-pressure superconductor beta'-(BEDT-TTF)(2)ICl2 at several pressures up to 12 GPa using the density-functional theory within the generalized gradient approximation (GGA). We have found that the calculated structure at ambient pressure agrees well with the experimental one, implying that GGA is reliable for the theoretical determinations of the crystal structure at high pressures. We show that the intermolecular interactions exhibit various and complex pressure dependence, contrary to the simple suggestions made so far. The width of the band crossing the Fermi level becomes almost twice at 8 GPa, and the dimensionality of the Fermi surface is affected significantly.