about setting the k points sampling

[xiaoling]

Sir
I want to repeat the work cited in https://quantumwise.com/support/tutorials/item/512-opening-a-band-gap-in-silicene-and-bilayer-graphene-with-an-electric-field. When use nA=nB=9 k-points, all is ok. But change the parameters nA and nB, I cannot get the right band structure. Why?

[Ulrik G. Vej-Hansen]

First, I suggest that you use the "new" documentation portal at docs.quantumwise.com. Any new and/or updated tutorials we make are placed here, such as a new version of the one you linked to: https://docs.quantumwise.com/tutorials/opening_a_band_gap/opening_a_band_gap.html

There is no guarantee that any specific k-point grid samples any specific (high-symmetry) point. In this case, a 21x21 k-point grid does not seem to sample the K-point directly, which leads to the observed shift. 

[xiaoling]

Thanks for your reply. But I don't understant how to choose the right k-poing samples. According to my understanding, if 21x21x1 can not repeat the results of 9x9x1, it means the k-points of 9x9x1 is not enough dense. Do you agree with me? So it really makes me confuged. 

[xiaoling]

In addition， I test the 18x18x1, which high-symmetry point should be in accordance with  9x9x1, but I cannot get the right band structure. Why?

[Ulrik G. Vej-Hansen]

We need to spend some time looking into this - I will get back to you as soon as possible.