# RE: [SIESTA-L] Problems of Siesta Calculation with Large Electric Field

```Dear Danny,

Thank you so much for the reply! It helped me a lot. I followed your
suggestions and my calculation is running properly now!```
```
Best,

Fanmiao

Fanmiao Kong
Department of Materials, Trinity College, University of Oxford
Tel: +44 (0)7529931806 / +86 13162054601
16 Parks Road, OX1 3PH, Oxford, UK

From: siesta-l-requ...@uam.es <siesta-l-requ...@uam.es> On Behalf Of Daniel
Bennett
Sent: 18 November 2021 21:30
To: siesta-l@uam.es
Subject: Re: [SIESTA-L] Problems of Siesta Calculation with Large Electric Field

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: siesta-l-requ...@uam.es<mailto:siesta-l-requ...@uam.es>
<siesta-l-requ...@uam.es<mailto:siesta-l-requ...@uam.es>> on behalf of Nick
Papior <nickpap...@gmail.com<mailto:nickpap...@gmail.com>>
Sent: 17 November 2021 22:07
To: siesta-l <siesta-l@uam.es<mailto:siesta-l@uam.es>>
Subject: Re: [SIESTA-L] Problems of Siesta Calculation with Large Electric Field

Hi,

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

Den ons. 17. nov. 2021 kl. 22.03 skrev Fanmiao Kong
<fanmiao.k...@materials.ox.ac.uk<mailto:fanmiao.k...@materials.ox.ac.uk>>:

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!

Cheers,

Fanmiao

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 (http://www.max-centre.eu/)

--
Kind regards Nick
```
```--
SIESTA is supported by the Spanish Research Agency (AEI) and by the European
H2020 MaX Centre of Excellence (http://www.max-centre.eu/)
```