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First principles calculations of mechanical properties of 4,4'-bipyridine attached to Au nanowires.

A first attempt is made to calculate the forces involved in the breaking of nanowires consisting of a molecule attached to nanosized metallic pieces. As a model system, we consider different Au nanowires connected by a 4,4(')-bipyridine or pyrazine molecule, for which density functional calculations were performed at different elongations. The geometry of the system was optimized for different forces applied. In all cases the calculated maximum forces were close to 1 nN, which is of the order of the experimental values, and smaller than the corresponding to the rupture of the Au-Au chain (1.5-1.6 nN). When 4,4(')-bipyridine is attached to Au monoatomic nanowire, the maximum force required to break the Au-Au bond may be lowered to values close to that obtain to break the Au-N bond, but when 4,4(')-bipyridine is attached to small Au clusters, the breaking of the nanowire takes place at the Au-N bond only.