FIRST-PRINCIPLES INTERATOMIC POTENTIALS FOR TRANSITION-METAL ALUMINIDES - THEORY AND TRENDS ACROSS THE 3D SERIES

In this paper the first-principles generalized pseudopotential theory (GPT) of transition-metal interatomic potentials [J. A. Moriarty, Phys . Rev. B 38, 3199 (1988)] is extended to AB binary compounds and alloy s. For general transition-metal (TM) systems, the GPT total-energy fun ctional involves a volume term, central-force pair potentials, and ang ular-force multi-ion potentials, which are both volume (Omega) and con centration (x) dependent and include all sp, sp-d, and d-d interaction s within local density-functional quantum mechanics. The formalism is developed here in detail for intermetallic systems where A is a simple metal and B is a transition metal and applied to the prominent specia l case of the transition-metal aluminides TMxAl1-x, where sp-d hybridi zation is especially important. Emphasis is given to the aluminum-rich 3d binary systems for x < 0.30, which appear to be well described at the pair-potential level without angular forces and for which the pres ent GPT potentials can be used directly in atomistic simulations. Volu me terms and pair potentials for all of the 3d aluminides have been ca lculated and their behavior with atomic number, Omega, and x is elabor ated through illustrative applications to the cohesive and structural trends across the 3d series. More extensive applications to the Co-Al and Ni-Al phase diagrams will be given elsewhere.