[Wien] twisted angle

[Rubel, Oleg]

Sharing my experience: After playing in VESTA with graphene, I became skeptical about prospects of arranging two layers (miss-oriented and stress free!) with periodic boundary conditions and a reasonable (for DFT) number of atoms. But maybe others are more lucky :)

Oleg

--
Oleg Rubel (PhD, PEng)
Department of Materials Science and Engineering
McMaster University
JHE 359, 1280 Main Street West, Hamilton, Ontario L8S 4L8, Canada
Email: rubelo at mcmaster.ca
Tel: +1-905-525-9140, ext. 24094
Web: http://olegrubel.mcmaster

________________________________________
From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of Gavin Abo <gsabo at crimson.ua.edu>
Sent: Tuesday, November 10, 2020 01:19
To: wien at zeus.theochem.tuwien.ac.at
Subject: Re: [Wien] twisted angle

Let's assume there are two sheets of graphene: sheet 1 and sheet 2.  If sheet 1 is place at a fixed position but sheet 2 is placed directly above it in the z direction and then rotated around the z axis with an angle Theta. Perhaps this is one definition of a twisted angle (Theta).

In other words, similar to what is seen in Figure 1 of the article "Twisted Bilayer Graphene: Interlayer Configuration and Magnetotransport Signatures" at the link:

https://doi.org/10.1002/andp.201700025

And similar to FIG. 1b and FIG. 4b in the article "Gap Opening in Twisted Double Bilayer Graphene by Crystal fields" at the link:

https://arxiv.org/abs/1910.10524v2

If that is the case, it seems like it would be a matter of geometry on how you would have to define your structure in case.struct.

It looks like such a structure with two sheets would require 2D-slabs with 2 layers separated by a vacuum.

WIEN2k has tools such as "x supercell" and "structeditor" that can help define 2D-slabs.

There is information in the mailing list archive [ http://susi.theochem.tuwien.ac.at/reg_user/mailing_list/ ] and on the Internet for these tools.  A few examples are as follows.

Slides 5-8: http://susi.theochem.tuwien.ac.at/onlineworkshop/PB-getting_started3.pdf
Slides 11-14 (Exercise 4): http://susi.theochem.tuwien.ac.at/events/ws2015/Exercises_15.pdf
http://susi.theochem.tuwien.ac.at/reg_user/faq/supercells.html
http://wien2k-algerien1970.blogspot.com/2019/01/practising-supercell-tool.html
https://wien2k-algerien1970.blogspot.com/2017/12/how-to-create-slab-structure-2d-of.html

Section "9.29 structeditor" in the WIEN2k 19.1/19.2 usersguide [http://www.wien2k.at/reg_user/textbooks/usersguide.pdf ] has "rotateatomlist" that you can read about that could of be interest for this.

Another tool that has been used by others is VESTA [ https://jp-minerals.org/vesta/en/ ]:

https://wien2k-algerien1970.blogspot.com/2017/12/how-to-construct-graphene-structure-and.html

However, slab calculation and vacuum are computationally expensive as you can read about in the following posts:

https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg06138.html
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg09158.html
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg13625.html

So setting up such a calculation might be a waste of time if you don't have access to computer hardware that is capable of doing such a calculation.

A single personal desktop/laptop computer in my experience tends to be insufficient when going beyond about simple unit cells and small supercells with only a few atoms.

It may be that a group of GB networked computers is needed:

https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg09334.html
https://social.technet.microsoft.com/wiki/contents/articles/2539.diy-supercomputing-how-to-build-a-small-windows-hpc-cluster.aspx
https://diybigdata.net/personal-compute-cluster-2019-edition/
http://www.ssanalysis.co.uk/blog/spreading-the-load-an-abaqus-cluster-blog

If that is not enough, a small rack or small high computing cluster (HPC) may be needed:

https://www.admin-magazine.com/HPC/Articles/real_world_hpc_setting_up_an_hpc_cluster
http://techcenter.wikifoundrymobile.com/page/Dell+Life+Cycle+Controller+features+for+High+Performance+Computing+Cluster+Deployment

It is also possible that may not be enough and a larger HPC may be needed for such a calculation:

https://uwm.edu/hpc/specifications-3/
https://hpc.uni.lu/systems/gaia/
https://www.isip.piconepress.com/projects/neuronix/html/neuronix_overview.shtml
https://wiki.anunna.wur.nl/index.php/Architecture_of_the_HPC
https://www.delltechnologies.com/resources/en-us/asset/offering-overview-documents/ready-bundle-for-hpc-research-solution-overview.pdf

It is of course difficult to generalize what would be needed because computer hardware is very diverse as can be seen by looking at the systems at the above links and the structures (e.g., having different number of atoms) and calculation parameters used vary computer resources for computation, such that an attempt at running the calculation is sometimes the easiest why to determine if it will compute or not [ https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg08136.html ].  One example of a parameter you may already be familiar with would be the number of k-points:

http://susi.theochem.tuwien.ac.at/reg_user/textbooks/WIEN2k_lecture-notes_2013/WIEN2k-getting_started.pdf (slide 10)
http://susi.theochem.tuwien.ac.at/reg_user/faq/kgen.html
https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg01053.html

Hopefully the above helps and good luck.

On 11/9/2020 6:32 AM, Brik Hamida wrote:
Dear

I am working on 2D structures and 2D heterostructures . I want to know if the twisted angle can be done using Wien2k code. If it is possible can someone explain how and thanks.

Best regards
Brik