Properties of the liquid-vapor interface of fcc metals calculated using the embedded atom method
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J. B. Adams Department of Materials Science and Engineering, University of Urbana, Illinois 61801
Minois-Urbana-Champaign,
S. M. Foiles Sandia National Laboratories, Livermore, California 94550
W. N. G. Hitchon Materials Science Program, University of Wisconsin-Madison, Madison, Wisconsin 53706 (Received 23 February 1989; accepted 5 November 1990)
The Embedded Atom Method (EAM) is used to compute density, internal energy, and structure factor for bulk liquids of the fee metals at several temperatures above and below the melting temperature. The calculated values are found to be in generally good agreement with experiment, although the volume expansion upon melting does differ by up to 50% from the expected result for some of the elements studied. The total energy of a liquid system with surfaces is calculated, and the results are compared with the bulk liquid results to determine the enthalpy and thickness of the liquid-vapor interface. Also, the surface tension is found for Cu near the melting temperature. The EAM values for surface enthalpy and surface tension are found to be smaller than experimental values, which is consistent with results for EAM calculations of the surface energy of crystalline solids.
I. INTRODUCTION The study of liquid metal surfaces poses a challenging problem both experimentally and theoretically. Experimental technique is made complex by the high temperatures at which most liquid metals exist, and results from different approaches show a wide range of values.1"4 Accurate computer models of liquid surfaces require hundreds of atoms, too many for first-principles techniques. Pair potentials and pseudopotentials have been used, but require a large volume-dependent term in order to describe the elastic properties of metals accurately.5 Their use in examining surfaces requires a detailed definition of where the surface ends in order to determine the contribution of this term to the total energy, but there is no unambiguous way to define this. Therefore, it is not clear how the surface will contribute to the volume-dependent term, and in many cases, a negative surface energy will result.6 The embedded atom method (EAM), developed by Daw and Baskes,7 has had great success in examining the properties of surfaces and defects. The EAM is based on density functional theory, in which the energy of an arbitrary configuration of atoms is a unique function of the electron distribution. The energy is subdivided into the embedding energy, which is the energy required to 'embed' each atom into the local electron density contributed by all other atoms, and a short298 http://journals.cambridge.org
J. Mater. Res., Vol. 6, No. 2, Feb 1991 Downloaded: 16 Mar 2015
range screened electrostatic pair interaction that accounts for electrostatic interactions. The total energy is written as: •Etotal = ^F(pi)
+ — X ^i(Ri)
(1)
where F(p) is the embedding energy, p is the total local electron density, calculated as a superposition of atomic electron densities, (R) is the screened electrostatic interaction, R i
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