Asked by maluneelambari on 2019-09-24

I am trying to do a transiesta calculation. In the transiesta calculation for the scattering region scf convergence ha obtained after 582 iterations. But ts-scf convergence has not achieved even after 1400 iteration.
DM.MixingWeight 0.05
DM.NumberPulay 6
MaxSCFIterations 2000

These are the parameters i have used.
Is it better to restart the system previous DM and TSDE or start from scratch by changing parameters?
Is force optimization occurs in scf cycle?
I tried to do the calculation with multiple restarting by using previous tsde and dm files. When I use the previous tsde file which was not converged it directly goes to transiesta convergence calculation and further satisfies the convergence criteria. But in those cases force seems to be very high.
What is the efficient method to achieve convergence in transiesta?
Is it increasing max scf iteration to a very big number or do multiple restart?

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Nick Papior (nickpapior) said : #1

1) always start TS calculations from previous TSDE files (this is described in the manual)
2) Always check your output for the ts-q row. Ideally the dQ column should be almost 0. If it is larger than 0.1% of your total number of electrons, then you really need to be careful.
3) Multiple restart is not very efficient. You need to play with mixing parameters. (there are no good values, trial and error is your best bet).

I am using siesta b3 version. It gives tsde file even before scf convergence has achieved. So it okay to restart with that tsde file(which is of the system not converged)?

Nick Papior (nickpapior) said : #3

Please use siesta-4.1-b4 version, do NOT use siesta-4.1-b3 version.

This is a trial and error experiment. You have to test this!

In the first set of transiesta calculation only scf got converged and transiesta doesn't. But when I restarted it with previous TDSE and DM ts-scf also got converged and tshs file has obtaines. But force seems to be huge
    Tot -2.011191 -2.787442 1.093283
(total foce in the output)
And it is very huge for atoms.
What is wrong here?

Nick Papior (nickpapior) said : #5

I don't know. Forces on electrodes and buffer atoms are incorrect. So you have to disregard those.

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