Fig. 12. Decomposition of the total thermal conductivity of finite-size models of v-SiO₂ into populations and coherences terms.

a Results for the small `192(G)' model. The dashed red line is the bare WTE conductivity computed at q = 0; the lack of perfectly degenerate vibrational modes in this disordered model and zero diagonal elements ($s=s^{\prime }$) of the velocity operator at q = 0 implies that the total bare WTE conductivity originates entirely from coherences. The solid green and blue lines are the populations and coherences rWTE conductivities computed on a 3 × 3 × 3 q mesh, their sum is the bulk limit of the total rWTE conductivity (dashed-dotted gray). b and c: results for the medium 1536(G) and large 5184(G) models, styles are the same as before. We highlight how the populations conductivity (green) decreases as the size of the model increases, such a decrease is compensated by an increase of the coherences conductivity; this implies that these different models have practically indistinguishable total thermal conductivities. In practice, in the 1536(G) and 5184(G) models the bare WTE computed at q = 0 reproduces the total rWTE conductivity.