Twisted Help

[yiwei zhao]

Hi~

I wonder how to get a bigger angle-structure (double layer MoS2) by using the Twister.py. I see that in the hex.table the angles are so small. I want to get a bigger angle, sch as ~40 degree or ~50 degree.

Thank you very much!

[Twister Help]

Hi Yiweide,

There are two ways to do this:

1. If you want to scan many structures quickly: See /path-to-Twister/FFRelaxation/mos2/. Take a look at near_0/near_60 folders.

--> In the no_relax/relax folder, you will find a script called "homo.sh".

Within the script homo.sh, uncomment the "printf "$latcon" | python $aux_files/hex_table_generic.py" line and comment out ""printf "$latcon" | python $aux_files/hex_table_least.py"".

--> In the aux_files/ folder set the angle range in hex_table_generic.py (change the line "sort_angles(100, 100, 40, 50, 'hex.table', 200)" to something like this) and run "python3 /path-to-aux-files/hex_table_generic.py". You will generate hex.table.

--> use the preferred indices from hex.table and run homo.sh. You can generate multiple structures with arbitrary twist angles. change "init" and "end" indices in homo.sh.

****

In simple words, the hex.table is generated with the general formula (np.arccos((m**2 + 4*n*m + n**2)/(2*(m**2 + n*m + n**2)))*180./np.pi, m and n can be any integer) rather than the specific one where |m-n|=1 is enforced. 

****

2. With get_ang.py. See for example :/path-to-Twister/examples/Homobilayer_hex/Mos2_withGetAng folder. Change the "strain_per" to a minimum and "theta_range" to the desired value.

Please let us know if this works for you.

Best regards,

Indrajit

[yiwei zhao]

Dear Indrajit,

Thank you so much for helping me solve this problem. And I have got the twisted structure  I want.

By the way, I have a question: Begin with the AB stacking basis_pos_crys and basis_pos_crys_layer2, I get a double layer MoTe2 with the twisted angle equals to 0 degree.  But I find that the generated POSCAR.vasp is three times to unitcell. Why is this?

Are the generated structures not the smallest structural units? This will be time-consuming in the process of optimizing the structure by DFT.

Bset.

Yiwei

[Indrajit Maity]

Hi Yiwei,

Typically we use the basis_pos* files obtained from first principles calculations and I have mostly used it to construct twisted bilayers (i.e. whenever there's a moiré pattern). Note that when you construct double layer MoTe2 with a twist angle of 0 degrees, you are simulating a bilayer (and not a twisted bilayer).

The moiré pattern you construct using the get_ang or FFRelaxations agrees with each other and gives a minimum area moiré lattice. You can compare yourself with MoS2 as an example.

Nevertheless, I will take a look sometime at the bilayer case that you pointed out.

Thanks,

Indrajit

 

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