[Wien] twisted angle

[Gavin Abo]

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 
<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 
<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
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