[QE-users] A question on the volume_factor flag in d3_tk.x

[Lorenzo Paulatto]

Hello Elio,
The problem is that tk is given for bulk per unit of volume. When you do a 2D material in plane waves, you need to put a lot of vacuum. The volume factor is used to make the value independent on the amount of vacuum. It can  is the ratio of the bulk uni cell to the 2d unit cell, or the ratio between the c axis in bulk and in the film, it is the same thing.

Please not that 2d materials are very tricky: the thermal conductivity from the quadratic band is integrable but diverging. Using some kind of regularization or a cutoff may be required.

Cheets



On June 15, 2023 8:48:16 p.m. GMT+02:00, Elio Physics <Elio-Physics at live.com> wrote:
>Dear all (and specifically Professor Paulatto),
>
>Sorry to bother you again with another question regarding the d3q code. To calculate the lattice thermal conductivity for 2D materials, we need to define a volume_factor =H/V. H is defined as the interlayer distance for the corresponding bulk material. If I understood correctly, let us say we have a 1H MoS2, we know that the bulk can be modeled as two layers (a  total of six atoms per unit cell). H would then be the distance between the upper S layer of the bottom MoS2 and the lower S layer of the MoS2 on top. Correct?
>
>
>Now what if we have a 1T 2D structure. Up to my knowledge, the bulk is modeled as one layer ( 3 atoms per unit cell).  In this case, what would H be ? The thickness of the structure?
>
>
>
>Regards
>
>Elie Moujaes
>Federal University of Rondonia
>Brazil
>Porto Velho
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