Dear Fanmiao,

I have done a few calculations with fairly strong fields. I don't think it is a 
bug, but rather it is just very difficult to converge the SCF loop when the 
field is very strong. Two things that helped me were:

  *   First, make sure that the SCF loop converges well at zero field. You'll 
need to test the different options like mixing weight and mixer history. Take a 
look in the manual, and this mailing list, since many people ask about this 
(myself included)
  *   When doing calculations with an electric field, chaining several 
calculations together via the density matrix and gradually increasing the field 
greatly improves the convergence: instead of trying to do E= 2 V/Ang with no 
input *.DM, do a calculation at zero field, then take the *.DM and use it as an 
input for a calculation with e.g. E = 0.5 V/Ang, then use the *.DM from that 
for E = 1.0 V/Ang, and so on until you get to the desired field strength. The 
smaller the step size in field strength, the easier the convergence will be, 
but you will require more calculations, so it is up to you to decide

Hope this helps,

Danny Bennett

From: <> on behalf of Nick 
Papior <>
Sent: 17 November 2021 22:07
To: siesta-l <>
Subject: Re: [SIESTA-L] Problems of Siesta Calculation with Large Electric Field


Could you attach a complete workable example (fdf and psf files)?

Den ons. 17. nov. 2021 kl. 22.03 skrev Fanmiao Kong 

Hi All,

I met some bugs when I do Siesta calculation under electric field. Sometimes 
the calculation doesn’t converge after 500 steps in a SCF cycle, or sometimes 
the hydrogen atoms in my structure are ionized. I attached the output file here 
where the calculation didn’t converge and I stopped it. I suppose this is 
because of the very large electric field ( between 1.5 – 2.1 V/Ang), since I 
don’t have this problem with electric field below 0.1 V/Ang. Does anyone know 
how to fix this problem?

Many thanks!



Fanmiao Kong

Department of Materials, Trinity College, University of Oxford

Tel: +44 (0)7529931806 / +86 13162054601

16 Parks Road, OX1 3PH, Oxford, UK

SIESTA is supported by the Spanish Research Agency (AEI) and by the European 
H2020 MaX Centre of Excellence (

Kind regards Nick
SIESTA is supported by the Spanish Research Agency (AEI) and by the European 
H2020 MaX Centre of Excellence (

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