YIELDING AND FRACTURE MECHANISMS OF NANOWIRES

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 tempe rature. The elongation under uniaxial stress is realized by consecutiv e 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. Thi s causes an abrupt decrease of the tensile force. Owing to the excessi ve strain at the neck, the original structure and atomic registry are modified; atoms show a tendency to rearrange in closed-packed structur es. In certain circumstances, a bundle of atomic chains or a single at omic chain forms as a result of transition from the hollow site to the top site registry shortly before the break. The wire is represented b y a linear combination of atomic pseudopotentials and the current is c alculated to investigate the correlation between conductance variation s and atomic rearrangements of the wire during the stretch. The origin of the observed ''giant'' yield strength is explained by using result s of the present simulations and ab initio calculations of the total e nergy and Young's modulus for an infinite atomic chain.