  We theoretically explore the influence of end-group chemistry (bond stiffness
and mass) on the interfacial thermal conductance at a gold-alkane interface. We
accomplish this using the Non-Equilibrium Green's Function (NEGF) coupled with
first principle parameters in Density Functional Theory (DFT) within the
harmonic approximation. Our results indicate that the interfacial thermal
conductance is not a monotonic function of either chemical parameters, but
instead maximizes at an optimal set of mass and bonding strength. This maximum
is a result of the interplay between the overlap in local density of states of
the device and that in the contacts, as well as the phonon group velocity. We
also demonstrate the intrinsic relationship between the Diffusive Mismatch
Model (DMM) and the properties from NEGF, and provide an approach to get DMM
from first principles NEGF. By comparing the NEGF based DMM conductance and
range of conductance while altering the mass and bonding strength, we show that
DMM provides an upper bound for elastic transport in this dimensionally
mismatched system. We thus have a prescription to enhance the thermal
conductance of systems at low temperatures or at low dimensions where inelastic
scattering is considerably suppressed.
