Hydrogen welding and hydrogen switches in a monatomic gold nanowire

Ab initio density-functional calculations are performed to study the interaction between a monatomic gold nanowire suspended between two gold tips and hydrogen, in the molecular, quasi-dissociated, dissociated, and atomic forms. Structural configurations, electronic states, vibrational modes, and electronic transport are investigated for several elongation stages of the wire, corresponding to the last conductance plateau (G approximate to 1 g(0), g(0) = 2e(2)/h) before breaking of the contact. We illustrate welding and restoration of electric conductance of a broken wire through the incorporation of an H-2 molecule, and an electric switching action resulting from structural fluctuations of an adsorbed molecule caused by mechanical forces applied to the wire.