  We derive expressions for energy flow in terms of lattice normal mode
coordinates and energy transmission involving reduced group velocities. With a
version of Landauer formula appropriate for lattice dynamic approach, the
phonon transmission coefficients and thermal conductance are calculated for two
kinds of acoustically mismatched junctions: different chirality nanotubes
(11,0) to (8,0), and Si-Ge superlattice structure. Our calculation shows a
mode-dependent transmission in nanotube junction and a resonantly modulated
ballistic thermal conductance in superlattice. The superlattice result suggests
a new interpretation of the experimental data. Our approach provides an
atomistic way for the calculation of thermal conduction in nanostructure.
