Embedded-atom-method Interatomic Otentials For Fcc Transition Metals Based On Lattice Inversion Method

Due to the high melting point, high hardness, good electrical and thermal conductivity, face-centered-cubic (fcc) transition metals Cu, Ag, Au and Pd are widely used in electricity power, communications, light manufacturing, construction, national defense, biocatalysis and so on. Although the great progress has been made in the preparation and synthetic routes in experiments for these four metals, there still require some understandings from the theory research. Espescially at the atomistic scale, the embedded-atom method (EAM) interatomic potentials originated from density functional theory (DFT) are playing the important role in large-scale atomistic simulations for structure-dependent performance of metals and alloys.In most of the previous work, the EAM potentials were started from prior selection of function forms with some adjustable parameters, and the potential parameters were obtained by fitting to the experimental data or calculations. This led to some uncertainty and arbitrariness which were inevitably involved by providing several sets of potential parameters. In order to avoid these shortcomings, it is necessary to find the new way to obtain the EAM potentials.In the present work, the functions of EAM potential were considered based on the Finnis-Sinclair (F-S) forms, the cohesive energy was calculated by first-principle calculation, and contributed by short-ranged pairwise potentials and long-ranged embedding energy, In terms of the stable structures, several two structures are introduced for metals Cu and Ag, but only single structures for Au and Pd; Using the multiple-lattice inversion technique, we finally obtained the pairwise potential and atomic electron density for the four metals.In order to test the validity and superiority of the present interatomic potentials, some molecular-mechanical simulations are performed and compared with experimental values and calculations from first-principle method and Johnson’s potential. The results show the present EAM potential not only well reproduce the static structural properties taken as the potentials data source from first-principle calculations, but also well give reasonable descriptions for the lattice parameters, elastic modulus, P-V equations, phonon spectrum, point defects energy and phase stability, and most of them are in better agreement with experimental observations or the calculated values by first-principle method than the calculation in terms of Johnson’s potential, especially the tranferrability of EAM potentials of Cu and Ag. The calculation for the energy of hcp structure is slightly lower than fcc, which is not in agreement with experimental values. That means the present potentials still requiring future inprovement.Further more, the property at high pressure and large-scale atomistic simulation are calculated. The elastic modulus at high pressure reveal the fcc stable structures of Cu and Au will be instable at120GPa and180GPa respectively. The simulated Cu nanowires show the amorphous will appear when the surface atoms increasing with the reducing of nanowire size. The molecular dynamic simulations for two kinds of Ag nanoparticles under different temperatures were also performed, and the result indicates that the melting points are550K and700K for cubic and Ino-decahedron nanoparticles, respectivcely.In general, the method for obtaining the present potentials has some advantages such as simple potential functions, parameter free and good transferrablity which can be generalized to a series of metals and non-metals. In addition, the high-pressure and nano-scale atomistic calculations show that the present EAM potential may be applied to explore the derivation of structures under extreme conditions base on molecular mechanics and dynamics simulations, and providing the detailed atomic pictures which are difficulty covered in the experiments.