Vibrationally induced flip motion of a hydroxyl dimer on Cu(110)

Recent low-temperature scanning-tunneling microscopy experiments [T. Kumagai et al., Phys. Rev. B 79, 035423 (2009)] observed the vibrationally induced flip motion of a hydroxyl dimer (OD)(2) on Cu(110). We propose a model to describe two-level fluctuations and current-voltage characteristics of nanoscale systems that undergo vibrationally induced switching. The parameters of the model are based on comprehensive density functional calculations of the system's vibrational properties. For the dimer (OD)(2), the calculated population of the high-and low-conductance states, the I-V, dI/dV, and d(2)I/dV(2) curves are in good agreement with the experimental results and underline the different roles played by the free and shared OD stretch modes of the dimer.