Large scale supercell calculations for forces around substitutional defects in NiTi

Abstract

Density functional calculations are used to investigate the interatomic forces that arise if Ti atoms are substituted by Ni or Cu defect atoms. For the experimentally found monoclinic B19’ ground state structure, these forces are calculated for the unrelaxed atomic positions by the Korringa–Kohn–Rostoker Green‐function method. The force field in the vicinity of the defects is markedly different in 32‐ and 256‐atom supercells while it is nearly the same in 256‐ and 2048‐atom supercells. This difference is explained by symmetry arguments and discussed as a possible explanation for the concentration dependent transition from the high‐temperature B2 phase to low temperature B19’ or strain glass phases.