  We present an approach to calculate ballistic phonon transport that combines
the atomistic Green's function (AGF) method with ab initio results. For the
inter atomic potential we use the harmonic approach. The equilibrium positions
of the atoms and the inter atomic force constants(ifcs) are calculated using
the ABINIT program package, which is based on density functional theory.
Therefore, the presented approach is parameter free. From the Green's function
of the system we determine the density of states as well as the transmission
function. The thermal conductance is obtained within the linear response
regime. We apply this approach to bulk ZnO and bulk ZnS. Transmission functions
for different transport direction for each material are presented. A comparison
of the transmission function shows, that a ZnO/ZnS interface could be a
promising phonon blocker. Adding such interfaces in ZnO or ZnS based
thermoelectric devices could therefore increase the figure of merit.
