[Pw_forum] Strange behavior of scf calculation under finite-field

[lan haiping]

Thank you, Axel.

My calculation is modified from example31, and the script is attached below.
The field strength i set for calculation is 1.0e-3 a.u.,  the same as all
examples implemented in Q.E.   I want to do a 'relax' calculation after a
'scf' calculation under finite-field, but  the calculation always cannot
reach a successful convergence after one or more 'bfgs' steps.

 Is there any trick to accelerate or reach  scf convergence ?  I have tried
several times with different schemes  , such as increasing bands number ,
adding smearing , or decreasing /increasing  mixing parameters.
Unfortranately ,  there seems unsuccessful.


Regards,

H.P

On 7/5/07, Axel Kohlmeyer <akohlmey at cmm.chem.upenn.edu> wrote:
>
> On Thu, 5 Jul 2007, lan haiping wrote:
>
> HPL> Dear All,
> HPL>
> HPL>   I am studying electric-enthalpy method implemented in pw.x with
> HPL> example31.  There are some problems i cannot solve by myself.
> HPL> Firstly,  when i set "ecutrho" explictly, calculations under
> finite-field
> HPL> are failed without any complain information, such as CRASH report. My
> server
>
> please provide an input that can reproduce this.
>
> HPL> is of 8GB memory, and no such crash for other scf calculations . I
> had tried
> HPL> 'cg' and 'david' methods, and cannot solve this  problems.
> HPL> Secondly,  when i set occupations to 'mv' smearing scheme with
> degauss=0.03
> HPL> a.u. , the scf calculation of finite-field situation
> HPL> is very difficult to reach convergence.  I have tried to increase or
>
> calculations under external field _are_ more difficult to converge.
> how does your field strength compare to the value in example31?
>
> HPL> decrease mixing_ndim,  but failed.  Besides, i have tried to increase
> HPL> nbnd , which seems no effect on scf convergence.  Would you please
> give me
> HPL> some suggestion on parameters setting for scf calculation under
> finite-field
> HPL> ?
>
> it would be much easier to detect problems or make suggestions,
> if you'd post the relevant part of your input file (or another
> input that has the exact same problem).
>
> cheers,
>    axel.
>
> HPL>
> HPL> Thanks for your time and attention . Any suggestion or comment is
> HPL> appreciated .
> HPL>
> HPL> Best Wishes,
> HPL> H.P
> HPL>
> HPL>
> HPL>
> HPL>
>
> --
> =======================================================================
> Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
>    Center for Molecular Modeling   --   University of Pennsylvania
> Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
> tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
> =======================================================================
> If you make something idiot-proof, the universe creates a better idiot.
>
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-- 
Hai-Ping Lan
Department of Electronics ,
Peking University , Bejing, 100871
lanhaiping at gmail.com, hplan at pku.edu.cn
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