  In contrast to the static operations of conventional semiconductor devices,
the dynamic conformational freedom in molecular devices opens up the
possibility of using molecules as new types of devices such as a molecular
conformational switch or for molecular data storage. Bistable molecules, with
e.g. two stable cis and trans isomeric configurations, could provide, once
clamped between two electrodes, a switching phenomenon in the nonequilibrium
current response. Here, we model molecular switch junctions formed at silicon
contacts and demonstrate the potential of tunable molecular switches in
electrode/molecule/electrode configurations. Using the non equilibrium Green
function approach implemented with the density-functional-based tight-binding
theory, a series of properties such as electron transmissions, I-V
characteristics in the different isomer-conformations, and potential energy
surfaces as a function of the reaction coordinates along the trans to cis
transition were calculated. Furthermore, in order to investigate stability of
molecular switches in ambient conditions, molecular dynamics (MD) simulations
at room temperature were performed and time- dependent fluctuations of the
conductance along the MD pathways were calculated. Our numerical results show
that the transmission spectra of the cis isomers are more conductive than trans
counterparts inside the bias window for all two model molecules. The
current-voltage characteristics consequently show the same trends.
Additionally, the calculations of time-dependent transmission fluctuations
along the MD pathways have shown that the transmission in cis isomers is always
significantly larger than that of trans counterparts showing that molecular
switches can be expected to work as robust molecular switching components.
