GROUND-STATE STRUCTURAL STABILITY OF ORDERED FCC-BASED AND BCC-BASED LI-AL COMPOUND UNDER FIRST AND 2ND NEAREST-NEIGHBOR PAIR APPROXIMATION

Self-consistent local density electronic structure calculations have b een performed on a series of ground state ordered superstructures of l ithium-aluminium alloys spanning the entire concentration range. These structures are based on both fee and bcc lattices under the first and second nearest neighbour pair approximation which is adequate to stab ilize all the stable and metastable phases of the Li-Al system. Using the efficient tight-binding linear muffin-tin orbital (TB-LMTO) method , we have calculated the volume dependent total ground state energies and the systematic trends in various cohesive and electronic propertie s at zero temperature, as a function of Li concentration. The predicte d heats of formation for all the different ground state superstructure s result in a representative stability profile, which shows that the L 1(2), B32 and DO3 structures are the most stable amongst various phase s having Al3Li, AlLi and AlLi3 compositions, respectively. Moreover, w e have parameterized the cohesive energies using the Connolly-Williams cluster expansion method and estimated the effective many-body intera ctions for the fee lattice in an octahedron-tetrahedron cluster approx imation, and for the bcc lattice in an irregular tetrahedron cluster a pproximation. These volume dependent but configuration (as well as con centration) independent interactions coming out of the TB-LMTO-CWM app roach are not only important for first principles calculation of phase diagram but are also useful for predicting the evolutionary path of o rdering processes. (C) 1996 Elsevier Science Limited.