Ag-Cu

Abstract: In order to investigate the phase separation behavior in Cu–Zr–Ag bulk metallic glasses (BMGs) on an atomic level, a modified embedded-atom interatomic method potential for the Cu–Zr–Ag system has been newly developed. A clear tendency of phase separation of Ag-rich phases could be observed in the supercooled liquid, in reasonable agreement with experimental information. The potential can be used for atomistic investigations of the effects of alloying element Ag on a wide range of amorphous properties of Cu–Zr BMG.

Abstract: A binary embedded-atom method (EAM) potential is optimized for Cu on Ag(1 1 1) by fitting to ab initio data. The fitting database consists of DFT calculations of Cu monomers and dimers on Ag(1 1 1), specifically their relative energies, adatom heights, and dimer separations. We start from the Mishin Cu–Ag EAM potential and first modify the Cu–Ag pair potential to match the FCC/HCP site energy difference then include Cu–Cu pair potential optimization for the entire database. The potential generated from this optimization method gives better agreement to DFT calculations of Cu monomers, dimers, and trimers than previous EAMs as well as a SEAM optimized potential. In trimer calculations, the optimized potential produces the DFT relative energy between FCC and HCP trimers, though a different ground state is predicted. We use the optimized potential to calculate diffusion barriers for Cu monomers, dimers, and trimers. The predicted monomer barrier is the same as DFT, while experimental barriers for monomers and dimers are lower than predicted here. We attribute the difference with experiment to the overestimation of surface adsorption energies by DFT and a simple correction is presented. Our results show that this optimization method is suitable for other heteroepitaxial systems; and that the optimized Cu–Ag EAM can be applied in the study of larger Cu islands on Ag(1 1 1).

Abstract: A new embedded-atom method (EAM) potential has been constructed for Ag by fitting to experimental and first-principles data. The potential accurately reproduces the lattice parameter, cohesive energy, elastic constants, phonon frequencies, thermal expansion, lattice-defect energies, as well as energies of alternate structures of Ag. Combining this potential with an existing EAM potential for Cu, a binary potential set for the Cu–Ag system has been constructed by fitting the cross-interaction function to first-principles energies of imaginary Cu–Ag compounds. Although properties used in the fit refer to the 0 K temperature (except for thermal expansion factors of pure Cu and Ag) and do not include liquid configurations, the potentials demonstrate good transferability to high-temperature properties. In particular, the entire Cu–Ag phase diagram calculated with the new potentials in conjunction with Monte Carlo simulations is in satisfactory agreement with experiment. This agreement suggests that EAM potentials accurately fit to 0 K properties can be capable of correctly predicting simple phase diagrams. Possible applications of the new potential set are outlined.