[QE-users] Phonon Dispersion of graphene

[Md. Jahid Hasan Sagor]

Hi,

Thank you for the response. I have some confusion. If I define atoms in a
unit cell and then define k1 k2 k3 (k points) it will indicate a 3D system
right? If I define k1 k2 1, it will indicate a 2D system in the xy plane, 1
1 k3 (1D system) and 1 1 1(0D system). Then why would the calculation be
considered computationally large if I define 10 nm width ( rather I reduce
my system size from infinite to 10 nm)? Can you explain it to me?

FOr example, graphene
Atomic Positions
C 0.3333333    0.666666     0.5
C 0.6666666    0.333333     0.5

K_Points
12 12 1 0 0 0

pw.x < scf.in > scf.out
ph.x <ph.in>ph.out
q2r.x < q2r.in >q2r.out
matdyn.x<matdyn.in>matdyn.out

This provides phonon dispersion for graphene which is infinitely long in
the x and y plane. If it works out for some reasonable time. Why does it
take time for the system which is infinitely long in x direction and y
direction to have a finite width of 10 nm (24 unit cells)?

Thank you

Best
Jahid

On Sat, Dec 24, 2022 at 5:31 AM PAULATTO Lorenzo <lorenzo.paulatto at cnrs.fr>
wrote:

> Dear Jahid, you have to decide precisely what you want, than you may be
> able to simulate it in different ways. A width of 10nm is probably too
> large for a direct DFT calculation of phonons, in this case you can use the
> phonons for the unit cell and add the finite size as a perturbation with
> Green function methods. I know a paper where this is done, but there are
> probably others, and other methods.
> https://hal.archives-ouvertes.fr/hal-03011389
>
>
> Hth
>
>
> LP
> ------------------------------
> *From:* users <users-bounces at lists.quantum-espresso.org> on behalf of Md.
> Jahid Hasan Sagor <md.sagor at maine.edu>
> *Sent:* Saturday, December 24, 2022 10:17:28 AM
> *To:* Quantum ESPRESSO users Forum
> *Subject:* [QE-users] Phonon Dispersion of graphene
>
> Hi,
>
> Please help if you can. I am trying to find out the dispersion relation of
> graphene. I know that to find out the relation I have to use pw.x, ph.x,
> q2r.x and matdyn.x. But the problem is, after applying all the packages, I
> might get a phonon dispersion relation of graphene which is infinitely long
> in x and y direction. However, in my model I am using a finite width of
> graphene around 10nm (24 unit cell in the vertical direction). Which
> command in QE can do this for me so that I can model a graphene which is
> infinitely long in x direction and 10 nm in y direction?
>
> Best Regards
> Md Jahid Hasan
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