On 6/15/23 21:12, Elio Physics wrote:
Dear professor Paulatto,
Thanks for the information.
1)Would that divergence produce negative line widths? I have been
trying to obtain some decent results for graphene but when the
smearing is above 1.0 , the code crashes stating that the linewidth is
negative! i tried to increase the grid dimension but in vain.
To get a negative linewidth it takes a seriously broken calculation, as
the last therm can mathematically be negative
But that would require that the population of the higher phonon (q'') is
higher than the lower phonon (q') as w'' = w+w' > w'.
Also a broken compilation of the code, or a bug, but to say anything I
would need a specific case to test and reproduce.
2) Is there a flag in the input that ensures regularization or one
that imposes a cutoff?
No, it has been done ad-hoc for the specific paper about 2D systems,
although I did not do those calculations, I'm not sure of the details.
It is very easily done in post-processing, if store_lw=.true. is used to
save the linewidths to file, using the matlab script recompute_sma.m, or
any home-made script. A bit more complicated in the exact minimization
method, setting a reasonable Casimir scattering length may be the best
bet. Exact algorithm is very expensive to converge anyway, because one
cannot use shifted grid (and symmetry is not exploited at the moment)
Thank you
------------------------------------------------------------------------
*From:* users <[email protected]> on behalf of
Lorenzo Paulatto <[email protected]>
*Sent:* Thursday, June 15, 2023 5:02 PM
*To:* Quantum ESPRESSO users Forum <[email protected]>
*Subject:* Re: [QE-users] A question on the volume_factor flag in d3_tk.x
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
<[email protected]> 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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Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
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people and expresses its concerns about the devastating
effects that the Russian military offensive has on their
country and on the free and peaceful scientific, cultural,
and economic cooperation amongst peoples
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Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
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