# k point for the electrode

Dear community :

I got the following warning with transiesta:

Electrode: Left has very few k-points in the semi-infinite direction, at least 20 is recommended.

For scf calculation, a convergence test is usually done for the kpoints. I have the following questions :

1. why is the k points in the semi-infinite direction important ?

2. how do we make sure that it converges? (are there simpler ways then redoing the transport calculations?)

Thank you for the replies.

## Question information

- Language:
- English Edit question

- Status:
- Answered

- For:
- Siesta Edit question

- Assignee:
- No assignee Edit question

- Last query:
- 2017-03-20

- Last reply:
- 2017-03-21

Nick Papior (nickpapior) said : | #1 |

1. The self-energies are constructed from the semi-infinite (periodic) direction in the electrodes. It is thus _very_ important that the electronic structure has converged along this direction. To be on the safe side we force the users to at least have 20 k-points. Use 100 if in doubt, the electrode calculation is a one-shot calculation, so do not try and limit the number of k-points here.

2. Like any other DFT calculation proper convergence tests are required. If you use very many k-points along the semi-infinite direction in the electrodes (>100) this should not need to be convergence tested. But, all the other parameters should be tested just as any other DFT calculation.

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