Expansion of the Applicability of the Modified Embedded Atom Method to Non-Bulk Systems

In order to expand the applicability of modified embedded atom methods (MEAMs) from bulk to non-bulk systems, a dimer reference MEAM (DR-MEAM) is proposed. In this method, a diatomic structure is selected as the reference structure and the parameters for Cu are determined from the properties of the equilibrium bulk structure and some clusters, in order to obtain a wide range applicability from the bulk to the non-bulk systems. In the determination of the parameters, the lattice constant, the binding energy, and the bulk modulus are used as the bulk properties and the binding energy, the bond length, and the bond angle of Cu _n (n = 2, 3, 4) are used as the clusters properties. Several other properties of Cu are calculated by the DR-MEAM and the parameters, and they are compared with experimental results and DFT results to examine the present method and parameters. It is found that they exhibit good agreements for many properties such as the lattice stability, the shear elastic constants, the vacancy formation energy, the surface energy of low index crystal surfaces, the binding energy of the Cu clusters (n ≥ 5), etc. It is suggested that the present method and parameters have a wider range of applicability than the conventional MEAMs. The DR-MEAM does not exhibit good agreement only for the bond angle of Cu₃ and Cu₄. This disagreement seems to suggest a theoretical limitation of the embedded atom method approximation.