Ab initio pseudopotential calculations for aluminum-rich cobalt compounds

First principles pseudopotential calculations with a plane wave basis set are performed for a variety of real and hypothetical Al-rich structures in the Al-Co system. The technical issues arising in the application of the plane wave pseudopotential method to these compounds, specifically the transferability and the energy convergence of the pseudopotentials, the broadening schemes for finite k-point sampling, and the implementation of the conjugate gradients algorithm for metallic systems, are discussed. The structural properties of fcc Al and AlCo in the CsCl (B2) structure are studied in detail, and found to be in good agreement with experiment and linear augmented-plane-wave method calculations. Results from first principles total energy calculations for the full set of structures considered are discussed in connection with recent pair potential calculations, trends in the electronic density of states, and the structural energetics of these intermetallic compounds, closely related to quasicrystals.