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Published online by Cambridge University Press: 01 February 2011
Several existing models of icosahedral quasicrystals (QCs) are improved upon and studied by ab initio electronic structure methods. The following approach is used to optimize the models: 1) interchange of atoms in the existing (skeletal) models based on available knowledge of the local atomic environments, and 2) subsequent relaxation of the atomic positions using forces determined via first principles density functional methods. After minimizing the total energy, we investigate the ground state, and compare calculated results with available photo-emission spectroscopy (PES) and Mössbauer spectroscopy data. Significant improvement with respect to the starting (skeletal) model is achieved in several cases. We also examine the validity of the concept of negative valences of the transition metal atoms in QCs as advanced by Friedel.