Ab initio based interface modeling for fully coherent precipitates of arbitrary size in Al alloys

An ab initio based atomistic model scheme for an approximate determination of the interfacial and strain energies for the entire interface of a fully coherent precipitate in a host lattice is presented. For each given presumed compositionally abrupt interface, the model incorporates the effect of the strain evolution along the interface by use of a sequence of supercells. Each cell in this sequence has been distorted to describe the local interface region in question with the optimal accuracy allowed by periodic boundary conditions. Together, the cells comprise a shell of nm thickness, enclosing the full interface and its strongly affected near vicinity. The computational demands for the scheme are connected with the number of atoms in a given interface region cell, i.e., no scaling with precipitate size occurs – other than the number of cells required. In practice, this allows performing calculations for essentially all precipitate sizes. The scheme has been tested for the case of the main hardening precipitate β″ in the Al–Mg–Si alloy system and compared quantitatively with presently available alternatives. Implementation in an atomic hybrid model scheme for a full description of the precipitate interface energy should be realistic.