  Ab-initio total energy calculations reveal benzene-dithiolate (BDT) molecules
on a gold surface, contacted by a monoatomic gold STM tip to have two classes
of low energy conformations with differing symmetries. Lateral motion of the
tip or excitation of the molecule cause it to change from one conformation
class to the other and to switch between a strongly and a weakly conducting
state. Thus, surprisingly, despite their apparent simplicity these Au/BDT/Au
nanowires are shown to be electrically bi-stable switches, the smallest
two-terminal molecular switches to date. Experiments with a conventional or
novel self-assembled STM are proposed to test these predictions.
