Extracting critical stress surfaces of pristine materials using deformation paths in MD simulations

ET Dubois and P Lafourcade and JB Maillet, COMPUTATIONAL MATERIALS SCIENCE, 258, 114073 (2025).

DOI: 10.1016/j.commatsci.2025.114073

Accurate simulation of deformation processes at the atomic scale is critical for predicting the mechanical response of materials and particularly the calculation of directional critical flow or yield stresses. This work presents a method for applying arbitrary deformation paths in LAMMPS while adhering to its convention that supercell periodic vectors a, b are aligned such that a coincides with the x-axis and b lies in the (x,y) plane. This method is relevant for solid materials with low crystal symmetry and for exploring arbitrary - non uniaxial - deformations in a limit of 100 % deformation. It is also designed to be used along with NVE conditions in which dissipative phenomena can arise. The first step of the method consists in generating the simulation frame tensor's time evolution upon any deformation, which may initially violate LAMMPS alignment constraints. This constraint is then overcome by the application of a rigid body rotation to realign the tensor with LAMMPS's convention, ensuring valid periodic boundary conditions. The resulting lengths and tilt factors of the rotated tensor are expressed analytically and applied to the simulation cell using the fix deform command. The present approach versatility is validated with the calculation of directional critical stresses for various pristine materials upon constant volume shear, tension and compression, demonstrating its effectiveness in simulations involving complex deformation scenarios and diverse crystal structures. The critical stress surface extracted from these simulations are finally analyzed as the fingerprint of all deformation mechanisms nucleating in the material.

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