Yielding and fracture mechanisms of nanowires

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Abstract
This paper presents a detailed analysis of atomic structure and force variations in metal nanowires under tensile strain. Our work is based on state of the art molecular dynamics simulations and ab initio self-consistent field calculations within the local density approximation, and predicts structural transformations. It is found that yielding and fracture mechanisms depend on the size, atomic arrangement, and temperature. The elongation under uniaxial stress is realized by consecutive quasielastic and yielding stages; the neck develops by the migration of atoms, but mainly by the sequential implementation of a new layer with a smaller cross section at certain ranges of uniaxial strain. This causes an abrupt decrease of the tensile force. Owing to the excessive strain at the neck, the original structure and atomic registry are modified; atoms show a tendency to rearrange in closed-packed structures. In certain circumstances, a bundle of atomic chains or a single atomic chain forms as a result of transition from the hollow site to the top site registry shortly before the break. The wire is represented by a linear combination of atomic pseudopotentials and the current is calculated to investigate the correlation between conductance variations and atomic rearrangements of the wire during the stretch. The origin of the observed “giant” yield strength is explained by using results of the present simulations and ab initio calculations of the total energy and Young’s modulus for an infinite atomic chain.