ELECTRONIC-STRUCTURE-BASED PAIR POTENTIALS FOR ALUMINUM-RICH COBALT COMPOUNDS

A method for calculating ''constant volume'' pair potentials in Al-ric h transition-metal compounds is presented. The method is based on a co mbination of a Green's-function analysis of the interaction between tr ansition-metal d shells, and a perturbative treatment of the Al and tr ansition-metal pseudopotentials. In addition to the d-shell interactio ns, the pair potentials include terms describing interactions between pseudopotentials on different atoms, as well as interactions between t he pseudopotential on one atom and the charge density induced by the d shell on another atom. The potentials are parametrized by use of both ab initio total-energy results and experimental inputs. The methodolo gy is tested by calculating the energies of many different structures at the Al-rich end of the Al-Co phase diagram. The potentials correctl y predict the sequence of complex phases that occurs with increasing C o content, with just one exception. The complex phases are favored rel ative to simpler fcc-based phases by a large energy due mainly to shor t-ranged spacing constraints. The Co-Co potential has a secondary mini mum at 4.4 angstrom which coincides with the Co-Co spacings in the com plex structures, and thus further enhances their stability.