Structure and phason energetics of Al-Co decagonal phases

We develop a model for Al-Co decagonal quasicrystals and approximants. Our model defines a large number of potential atomic positions. These sites are populated by two atomic species that interact with each other through electronic-structure-based pair potentials. Monte Carlo simulation of the model produces realistic atomic configurations for Al-Co alloys in the temperature and composition ranges where a metastable decagonal quasicrystal exists. The resulting structures generally consist of packings of space by pentagonal bipyramid clusters. Projections of the centres of these clusters form tilings of hexagons, boats and stars. We identify atomic displacements associated with phason fluctuations. We note a distinction between 'simple' phason hops involving predominantly Al atom motion and 'collective' phason flips that transport the Co atoms.