Structural distortions in Al F3: A test for density-functional methods

The crystal structure of Al F3 at high temperatures has a simple cubic lattice. Below ∼730 K, the structure transforms to a rhombohedral (α -phase) structure with R 3̄ c symmetry due to an unstable R5- phonon. Density-functional based methods, from the least accurate rigid-ion model to highly accurate all-electron Kohn-Sham models, yield the triply degenerate R5- phonon that becomes unstable with decreasing volume at some critical volume Vc. Significant variations for Vc and the equilibrium volume V0 among the models lead to large uncertainties for the energy differences between the cubic and rhombohedral structures, indicating that present density-functional models are not reliable for accurate quantitative results in this case. © 2007 U.S. Government.

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Author Michael J Mehl Thomas Lord Department of Mechanical Engineering and Materia ...