Fracture behavior of lithium single crystal in the framework of (semi-)empirical force field derived from first-principles


DOI: 10.1088/0965-0393/23/4/045008

An approach to derive, from first-principles data, accurate and reliable potentials in the modified embedded-atom method in view of modeling the mechanical behavior of metals is presented in this work and applied to the optimization of a potential representative of lithium (Li). Although the theoretical background of the modified embedded-atom method was considered in this work, the proposed method is general and it can be applied to any other functional form. The main feature of the method is to introduce several path transformations in the material database that are critical for plastic and failure behavior. As part of the potential validation, path transformations different from the ones used for the parameterization procedure are considered. Applied in the case of Li, the material database was enriched with the generalized stacking fault energy curve along the <111> -direction on the 1 1 0-plane, and with the traction-separation behavior of a 1 0 0-surface. The path transformations used to enrich the material database were initially derived from first-principles calculations. For validation, the generalized stacking fault energy curves along the <111> -direction on the 1 1 2-and 1 2 3-planes were considered for plasticity, while traction-separation behavior of 1 1 0 and 1 1 1-planes were considered for failure behavior. As part of the validation procedure, the predictions made in the MEAM framework were validated by first- principles data. The final potential accurately reproduced basic equilibrium properties, elastic constants, surface energies in agreement with first-principles predictions, and transition energy between different crystal structures. Furthermore, generalized stacking fault energy curves along the <111> -direction on the 1 1 0, 1 1 2, and 1 2 3-planes, and tensile cohesive stress, characteristic length of fracture, and work of separation of a 1 0 0, 1 1 0, and 1 1 1 surfaces obtained in the MEAM framework compared well with first- principles predictions. It also predicts good elastic constants for a crystal structure different than the one used for the fitting of the potential and the other four path transformations. The potential was tested for failure behavior using a full atomistic setup, and in addition of being qualitatively correct, the stress intensity factor for different crack orientations was found to be in agreement with the theory of Rice (1992 J. Mech. Phys. Solids 40 239-71) within an error of 10%. Finally, the optimized Li-MEAM potential is expected to be transferable to different local environments encountered in atomistic simulations of lattice defects.

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