Significance of Buffer Regions

Asked by Emerald James on 2019-08-18


What is the significance of the buffer region in transiesta calculations? Isn't the measurement taken between the left and the right electrodes? The transiesta manual specifies that the buffer region helps in getting a better initial Hamiltonian. But adding buffer region significantly complicates my calculations and the convergence rate is too slow.

Should I place buffers on left side of the left electrode and right side of the right electrode or can I combine them on one side? Is there any formula to get the ideal number of buffer layers or is it trial-and-error?

Also, should I specify the same buffer region for my individual electrode calculations as well? Currently I'm specifying buffer only for my device calculation.

NB: I am using Siesta 4.1-b4


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Nick Papior
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Best Nick Papior (nickpapior) said : #1

1) Using buffer atoms should only improve convergence in the TS SCF cycle. So if this is not the case, then probably you are doing something wrong.

2) Buffer atoms are NOT part of the TS calculation. So they need to be placed on the other sides of the ELEC-DEVICE-ELEC geometry.

3) Buffer atoms has no influence of electrode calculations. They are *totally* unrelated.

Emerald James (emarald-james) said : #2

Thanks Nick Papior, that solved my question.