BFS strain energy

The BFS strain energy can be computed by any method appropriate for the calculation of pure element crystals. Due to its consistency with the determination of the chemical energy contribution, we choose the ECT [25,26] for its computation. 

Following the guidelines described above for the implementation of ECT, we now apply this formalism to the calculation of the BFS strain energy contribution, ef, of atom i. To do so, the ECT perturbation equation is written in terms of the distances rj between atom i and its nearest- and next-nearest-neighbors. 

Once the lattice parameter of the (strain) equivalent crystal, /, is determined, the BFS strain energy contribution is computed using the UBER [27], which contains all the relevant information concerning a single-component system ... 

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