Force fluctuations and localized states at point contacts

The effect of atomic and electronic structure on mechanical properties of a piece of sodium nanowire is studied with a total-energy method based on the density functional theory. We find that adiabatic elongation or compression of the wire results in discrete jumps in total energy due to a correlated rearrangement of electron states and atomic structure, and the resulting force shows oscillations in the nanonewton range. Furthermore, our results indicate that under certain conditions the break contact could support well-localized electron states. We discuss the results in connection with recent experiments and calculations on extended nanowires