Structural stability and lattice defects in copper:<i>Ab initio</i>, tight-binding, and embedded-atom calculations

TLDR

The other EAM potential was previously constructed using a traditional fitting scheme. The study evaluates whether EAM potentials and TB methods can reliably predict energies and stability of nonequilibrium Cu structures. The authors compare two EAM potentials—one newly fitted with extensive ab initio data and another traditional—and apply them, along with TB, to model epitaxial Cu films on fcc or bcc substrates. The results show excellent agreement among ab initio, TB, and EAM calculations, confirming that both TB and EAM can reliably predict Cu structure energies and stability; bcc, simple cubic, and diamond Cu are elastically unstable, while hcp and 9R are metastable, and epitaxial Cu films on fcc or bcc substrates adopt deformed fcc or hcp structures but cannot stabilize bcc.

Abstract

We evaluate the ability of the embedded-atom method (EAM) potentials and the tight-binding (TB) method to predict reliably energies and stability of nonequilibrium structures by taking Cu as a model material. Two EAM potentials are used here. One is constructed in this work by using more fitting parameters than usual and including ab initio energies in the fitting database. The other potential was constructed previously using a traditional scheme. Excellent agreement is observed between ab initio, TB, and EAM results for the energies and stability of several nonequilibrium structures of Cu, as well as for energies along deformation paths between different structures. We conclude that not only TB calculations but also EAM potentials can be suitable for simulations in which correct energies and stability of different atomic configurations are essential, at least for Cu. The bcc, simple cubic, and diamond structures of Cu were identified as elastically unstable, while some other structures (e.g., hcp and 9R) are metastable. As an application of this analysis, nonequilibrium structures of epitaxial Cu films on (001)-oriented fcc or bcc substrates are evaluated using a simple model and atomistic simulations with an EAM potential. In agreement with experimental data, the structure of the film can be either deformed fcc or deformed hcp. The bcc structure cannot be stabilized by epitaxial constraints.