Atomistic computation of liquid diffusivity.pdfVIP

PHYSICAL REVIEW B, VOLUME 65, 214106Atomistic computation of liquid diffusivity, solid-liquid interfacial free energy, and kinetic coefficient in Au and Ag J. J. Hoyt 1 and Mark Asta 2 1 Sandia National Laboratories, MS 1411, Albuquerque, New Mexico 87185 2 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 ~Received 21 December 2001; published 3 June 2002! Molecular-dynamics simulations using interatomic potentials of the embedded atom method have been performed on pure Ag and Au to compute materials parameters which are necessary for continuum modeling of dendritic solidification. The liquid state diffusion coefficient has been determined for temperatures in the vicinity of the melting points and good agreement with experimental data available for Ag is found. The kinetic coefficients for Au and Ag have been determined by monitoring the velocity of the solid-liquid interface as a function of undercooling. Rates of crystallization for the 100 and 110 directions agree well with a model proposed by Broughton, Gilmer and Jackson @Phys. Rev. Lett. 49, 1496 ~1982!# whereas the 111 direction exhibits a slower growth rate consistent with the presence of stacking fault clusters on the solid-liquid bound- ary, which anneal out during solidification. The solid-liquid interfacial free energy and its anisotropy have been obtained for Ag and Au by monitoring equilibrium fluctuations in the interface position. The fluctuation spectrum technique allows for an accurate determination of very small anisotropies in the interfacial energy and we find an anisotropy factor 1.060.3% for Ag and 1.660.3% for Au. DOI: 10.1103/PhysRevB.65.214106 PACS number~s!: 64.70.Dv, 81.30.FbI. INTRODUCTION In recent years it has become evident that the phase field method is the ideal technique to model the complex mor- phologies that form during dendritic solidification. The ad- vantage of the phase field model stems from the fact that the method was desig