Phonon transmission sprectrum

[Aun]

Hi,
I am trying to calculate phonon transmission sprectrum using VNL-ATK2016.4.
Regarding calculator, use combining two potentials Tersoff and Lennard Jones as described in tutorial. But phonon transmission sprectrum result is zero for all frequency. I would appreciate if someone could correct this error.
I attached my py file

[Julian Schneider]

I would guess the problem comes from the fact that the Tersoff-potential only describes the local bonded interactions within the graphene-layers, but does not account for the longer-ranged dispersion interactions between adjacent layers. This is  a known short-coming of Tersoff- and similar potentials. If there is no interactions between adjacent layers, then phonons cannot be transmitted across different layers.
This is typically corrected by adding a Lennard-Jones potential between Carbon-atoms, that accounts for the dispersion interactions, as e.g. in http://dx.doi.org/10.1103/PhysRevB.88.045444 .