Practical approach to thermal conductivity calculations of small SiO2 samples

We compute the thermal conductivity of amorphous SiO ₂ combining density functional theory calculations and lifetime models. The supercell we use to represent amorphous SiO ₂ is small, 78 atoms. We show that this rudimentary model is nevertheless sufficient to reproduce the temperature dependence of the thermal conductivity from 0.1 K to 1000 K if we use a lifetime model at low frequencies accounting for Rayleigh scattering, the absorption of phonons by two levels systems and structural relaxations. The necessary conditions needed to observe the plateau in the thermal conductivity around 10 K are also discussed according to this model.