Author Topic: k-points for transport calculation  (Read 94 times)

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Offline smd

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k-points for transport calculation
« on: July 13, 2019, 13:00 »
Why we need large k-points for transport calculation as the semi-infinite electrodes contain self-energies? How many k-points in the transport direction will be required for a defected CNT with pristine CNT as an electrode?

Offline Petr Khomyakov

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Re: k-points for transport calculation
« Reply #1 on: July 15, 2019, 09:12 »
It is required to accurately compute the Fermi energy in the electrodes. It is impossible to say exactly how many points you need, as it is a matter of convergence tests. Typically, if you have convergence issues with SCF device calculation, one of the possible reasons for that is inaccurately-computed Fermi level. In general, one should also converge the k-point sampling in the lateral directions as well - for CNT, that would just mean that you should have sufficiently thick vacuum padding around the tube to avoid spurious interaction between periodic images of CNT.

Offline smd

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Re: k-points for transport calculation
« Reply #2 on: July 16, 2019, 06:37 »
Thank you sir. I am getting the same results for transport calculations even if I am increasing the k-points in the lateral direction or keeping it 1.

Offline Petr Khomyakov

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Re: k-points for transport calculation
« Reply #3 on: July 16, 2019, 22:33 »
For modeling a single CNT, you should use a single (Gamma) k-point in the lateral directions, and check if the results converge with respect to vacuum padding thickness.