  Using first-principles approaches we investigate local heating and the
inelastic contribution to the current for various alkanethiols sandwiched
between metal electrodes. In the absence of good heat dissipation into the bulk
electrodes, we find that the local temperature of the alkanethiols is
relatively insensitive to their length. This is due to the rates of heating and
cooling processes scaling similarly with length. On the other hand, when
considering heat dissipation into the bulk electrodes, the local temperature of
alkanethiols decreases as their length increases. We also find that the
inelastic scattering profile displays an odd-even effect with length which
compares well with experimental results. This effect is due to the alternating
direction of the CH3 group motion with respect to current flow with increasing
C atoms in the chain, and is very sensitive to the structure of the
carbon-sulfur-gold bond. Inelastic scattering profiles can therefore help
illuminate the bonding configuration of molecules to metallic surfaces.
