optimization of bilayer ZGNR (DFT & DFTB)

[MaryamNazirfakhr]

Hello

I use ATK 2013 and i'm trying to optimize a billayer ZGNR. i've used DFT and DFTB methods and in both cases the result of optimization is something like the attached picture (http://8pic.ir/images/f6x8dz50sqxwos2oq2d3.png). The mesh cut-off and k-point sampling are set to 150Ryd and (5, 5, 5) respectively. Could u please tell me why the optimized bilayer structure is somehow bended? Is there any problem? If yes, What is the solution?

Thank you

[Jess Wellendorff]

It's hard to say from the image. Could you provide the script used for geometry relaxation?

[MaryamNazirfakhr]

I use DFT.

Calculator:
cut-off : 150Ryd
k-point sampling : 5,5,5
Tolerance : 0.0001
max step : 500

OptimizeGeometry:
default

Thanks

[Jess Wellendorff]

If you intend to do a true bilayer structure, one of the unnit cell directions must be non-periodic. But you use 5 kpoints along all directions. One kpoint should be enough along the non-periodic direction. Apart from that, I see no problems with your approach.

[danial]

Hi
i have the same problem, but I don't have any problem with making the Bilayer nano ribbon, my problem is shifted bilayer.
when you shift the bilayer, your structure miss the periodic condition, (semi- periodic).and use H to passivate the dangling band. finally use optimization geometry. but the result is not acceptable and is cluttered.
so how can optimize these structures?(with the different overlap).
thanks

[Jess Wellendorff]

I will be alot easier for me to advise if you upload the structure you are working with.