Ab Initio studies of the electronic structure and energetics of bulk amorphous metals
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I.
INTRODUCTION
BY now, a large number of compositions have been found that exhibit bulk amorphous behavior; some of the earliest found include Zr0.413Ti0.137Cu0.125Ni0.10Be0.225,[1] [2] La0.55Cu0.10Ni0.05Co0.05Al0.25, Zr0.60Cu0.15Ni0.10Pd0.05Al0.10,[3] Zr0.525Cu0.179Ni0.046Ti0.05Al0.10,[4] Zr0.57Cu0.154Ni0.026Nb0.05Al0.10,[4] and Ni0.4Pd0.4P0.2.[5,6] Many bulk amorphous metals (BAMs) have excellent properties: high strength (;2 GPa); ductility in compression; low coefficient of friction; high wear resistance; high corrosion resistance; low shrinkage during cooling; extended superplastic range between the glass transition temperature, Tg, and the recrystallization temperature, Tx; and almost perfect as-cast surfaces. It is important to understand why these glasses form at such low cooling rates and how alternative compositions can be similarly stabilized. In general, the understanding of the structure, properties, and required cooling rates for BAMs is hindered by the large number of constituents in the typical alloy. Thus, from the theoretical point of view, the two BAM systems, Ni0.4Pd0.4P0.2[5,6] and Zr0.6Al0.15Ni0.25,[7] are particularly attractive in that they contain only three elements yet display the important characteristics of this class of materials. Furthermore, the thoroughly studied structure of related binary glasses provides a useful starting point for theoretical investigation.[8,9] Much of the progress in the calculation of ground state properties of crystalline metals can be attributed to the local D.M.C. NICHOLSON, Senior Research Scientist, G.M. STOCKS, Corporate Fellow, and W.A. SHELTON, Research Scientist, are with the Oak Ridge National Laboratory, Oak Ridge, TN 37831-6114. YANG WANG, Senior Computational Scientist, is with Pittsburgh Super Computing Center, Pittsburgh, PA 15213. J.C. SWIHART, Professor, is with the Physics Department, Indiana University, Bloomington, IN 47405. This article is based on a presentation made in the ‘‘Structure and Properties of Bulk Amorphous Alloys’’ Symposium as part of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10–11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees, and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory. METALLURGICAL AND MATERIALS TRANSACTIONS A
density approximation (LDA) to density functional theory[10] and translational symmetry. Density functional theory reduces the many-electron problem, which is intractable for all but the simplest systems, to a one-electron problem with no approximation. In practice, the density functional equations are solved numerically within some approximation, typically the LDA. Translational symmetry allows the further reduction of the one-electron, but many atom, problem to an N atom problem, where N is the number of atoms in the periodically repeated unit cell. In conventional electronic (band) structure methods, the si
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