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The charge transfer salts κ-(BEDT-TTF)2X with X=Cu2(CN)3, Cu(SCN)2, Cu[N(CN)2]Cl and Cu[N(CN)2]Br have been intensely discussed as they have a fascinating phase diagram involving superconducting and spin liquid phases. We employ density functional theory calculations in order to study the underlying Hamiltonian and extract the relevant hopping parameters for use in manybody model calculations. For the system with X=Cu2(CN)3 which possibly represents a realization of a 2D quantum spin liquid, we carefully prepare equilibrium structures at ambient and elevated pressure using constant pressure Car Parrinello ab initio molecular dynamics calculations on the basis of the projector augmented wave method. We determine the hopping parameters of the underlying Hubbard Hamiltonian using tight binding fits to the calculated band structures. We find that increasing pressure reduces the frustration of the model. We find some corrections to the semiempirical parameters that have so far been considered for these systems. |
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