Effects of local geometry distortion at the Al/Al₂Cu interfaces on solute segregation

Interfaces in materials play a critical role in a wide range of functional properties. The heterophase semicoherent interface is one of the most difficult systems in density functional theory (DFT) simulations. We have studied the segregation energies of different solutes (Si, Mg and Zn) at the Al/Al2Cu (semi)coherent interfaces based on the linear combination of atomic orbitals (LCAO). Our DFT-LCAO computed segregation energies of solutes at the Al/Al2Cu coherent interface are in good agreement with the DFT-PAW calculations. However, at the Al/Al2Cu semicoherent interface, results from the LCAO calculations are significantly different to those obtained using the PAW method. The local geometry distortion in the semicoherent interface region significantly influences the solute energetics. Considering the distortion, the segregation energies of solutes well explain the trend of the experimentally measured solute concentrations, such as the higher solute Si concentration at the semicoherent interface than that at the coherent interface, and the similar Si concentration across the semicoherent interface. The lattice mismatch effect on the solute segregation energy is investigated as well. At low lattice mismatch (0.25%), the segregation energies of Si and Mg are almost compatible. Our results shed light on improving the theoretical predictions for interfaces to determine accurate functional properties.