Simplified pseudopotential expansion theory for Al-Li alloys

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A new pseudopotential expansion theory is developed for nearly-free-electron alloys. This theory includes local-density-dependent corrections to the usual pair potentials, to take into account long-wavelength charge-density fluctuations. A simplified treatment of the nonlocality of the pseudopotential is presented as well. Using this theory, the heat of formation and lattice constant are calculated for several ordered and disordered phases of Al-Li alloys. The importance of the local-density correction and the nonlocal pseudopotential terms to the atomic bonding in these alloys is analyzed, and the results are compared with experiments. The dominant exothermic contribution to the heat of formation comes from the nonlocality of the Li pseudopotential. Inclusion of the local-density and nonlocal pseudopotential terms results in considerably improved heats of formation. The concentration dependence of the calculated heats of formation and ordering energy is consistent with experiment and more accurate density-functional band-structure calculations. The results for the lattice constants of the ordered compounds agree well with experiment, and the experimentally observed lattice contractions of the solid solutions are also found. However, the failure of our method in constructing an accurate phase diagram from the calculated heats of formation indicates that further improvements, including higher-order terms in the strong Al pseudopotential, are needed.

Original languageEnglish
Pages (from-to)980-987
Number of pages8
JournalPhysical Review B
Issue number2
StatePublished - 1989


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