Analytic embedded atom method potentials for face-centered cubic metals
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Analytic embedded atom method potentials for face-centered cubic metals S. S. Pohlong and P. N. Rama) Department of Physics, North Eastern Hill University, Shillong, 793022, Meghalaya, India (Received 10 July, 1996; accepted 27 August, 1997)
The universal form of embedding function suggested by Banerjea and Smith together with a pair-potential of the Morse form are used to obtain embedded atom method (EAM) potentials for fcc metals: Cu, Ag, Au, Ni, Pd, and Pt. The potential parameters are determined by fitting to the Cauchy pressure sC12 2 C44 dy2, shear constant GV sC11 2 C12 1 3C44 dy5, and C44 , the cohesive energy and the vacancy formation energy. The obtained parameters are utilized to calculate the unrelaxed divacancy binding energy and the unrelaxed surface energies of three low-index planes. The calculated quantities are in reasonable agreement with the experimental values except perhaps the divacancy energy in a few cases. In a further application, lattice dynamics of these metals are discussed using the present EAM potentials. On comparison with experimental phonons, the agreement is good for Cu, Ag, and Ni, while in the other three metals, Au, Pd, and Pt, the agreement is not so good. The phonon spectra are in reasonable agreement with the earlier calculations. The frequency spectrum and the mean square displacement of an atom in Cu are in agreement with the experiment and other calculated results.
I. INTRODUCTION
The accuracy of computer simulation studies of metallic crystals has greatly increased with the replacement of widely used empirical pair potentials1–9 by these semi-empirical potentials based on density functional theory using the effective medium4 or quasi-atom approach.5 Ever since the introduction of embedded atom method by Daw and Baskes,6,7 the method has been widely used for a variety of problems ranging from perfect lattice phonons to highly distorted defect structures, including impurities, alloys, surfaces, and fractures8 and crack tips.9 A closely related model (N-body potential) has been developed by Finnis and Sinclair10 for bcc (body-centered cubic) metals based on a second-moment approximation to tight binding theory. As is clear from the work of Daw and Baskes6,7 and of Foiles et al.,11 there is tedious numerical fitting to obtain the parameters and functions required for the model, and all results must be obtained by detailed computation. Although once the parameters and functions are determined for a particular metal, the same set can be used for the study of various properties of the metal, including those which were really intractable by pair potential approach; nevertheless, the use of these potentials and functions is not very straightforward or convenient, since one has to have a detailed table for a)
Present address: Institute of Engineering Technology, Rohilkhand University, Bareilly 243006, Uttar Pradesh (UP), India. J. Mater. Res., Vol. 13, No. 7, Jul 1998
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