Self-consistent embedding quantum mechanics/molecular mechanics method with applications to metals

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We present a quantum mechanics QM/molecular mechanics MM method for coupling Kohn-Sham density-functional theory with classical atomistic simulations based on a self-consistent embedding theory. The formalism and numerical implementation of the method are described. The QM/MM method is employed to study extended defects—a grain boundary and an edge dislocation in Al by focusing on hydrogen H-defect interactions. We find that it is energetically more favorable for H impurities to segregate at the grain boundary and the dislocation core as opposed to the bulk. We provide direct first-principles evidence that both the grain boundary and the dislocation could serve as a “pipe” to accelerate H diffusion and shed light on the corresponding atomistic mechanisms. The results demonstrate that the QM/MM method is a powerful approach in dealing with extended defects in materials.