Comments welcome via email:
There has been considerable experimental and theoretical interest in synthetic materials formed from charge transfer salts of BEDT-TTF (bis-ethylenedithio-tetrathiafulvalene). Three crystalline formsof (BEDT-TTF)·PF6 have been identified experimentally, and labeled δ, ε, and ζ. We have modeled these three materials using first-principles self-consistent field methods, to determine the optimal geometrical parameters, the densities of state, and electron density contour plots for states near the Fermi level. The ε and ζ crystals are found to be metallic, while the δ crystals, with twice as many molecules per unit cell, are found to be insulating. By contrast, experimental conductivity and optical measurements for the ζ material suggest a Mott insulator behavior. We examine the Hubbard model for this system to understand both the Mott insulating behavior and the failure of the self-consistent field methods to model it.