QuantumATK Forum
QuantumATK => General Questions and Answers => Topic started by: Dipankar Saha on September 25, 2015, 09:11
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Hello,
I wanted to know_
Sometimes, while finding Tph for a nano ribbon...it is suggested to go with the Dij having a,b,c ~ 1x1x1 (custom)..../ What does this 1x1x1 mean? { I wanted to mean that... how the cell gets repeated and perturbed in that case? }
Thanks in advance ... :)
Best_
Dipankar
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What do you mean "it is suggested" ?
A repetition of 1x1x1 for the DynamicalMatrix calculation means no repetition at all. There should never be any repetition along non-periodic directions. This means that:
a) For 1D devices like nanotubes and nanoribbons, the repetition should be 1x1x1.
b) For 2D devices, like nanosheets that are periodic along B, the repetition should be 1 x N x 1, where N = 3 or 5 or 7 or 9, etc.
c) For 3D devices, which are periodic along both A and B, the repetition should be N x M x 1.
Note that the "automatic" repetition option sometimes selects repetition > 1 along non-periodic directions. This happens when the distance to the supercell side along that direction is relatively small. In that case. Manually set the repetition. That is the correct approach, and also saves considerable computational time.
Finally, for phonon calculations on bulk configurations (not devices) the repetition should usually be non-zero along all directions: N x M x K.
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Perhaps, you also said the same thing (point (a) ).....what that I was telling.... and can be found from a previous discussion too__
http://quantumwise.com/forum/index.php?topic=3447.15
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Anyways....thanks a lot Jess for the reply !!! :)
Best_
Dipankar