[Pw_forum] starting_magnetization problem

[Gabriele Sclauzero]

On 07/25/2010 07:29 AM, Weyl Fang wrote:
> Dear all,
>
> Recently i want to do a spin polarization calculation.

For a metal or an insulator?

> After I read the
> pw.x input file description, i know if i set the tot_magnetization to
> unspecified the amount of electronic magnetization is determined during
> the self-consistent cycle. So i set the tot_magnetization to
> unspecified. But when i execute pw.x, i get a error message some
> starting_magnetization MUST be set. But i get the message" If you fix
> the magnetization with "tot_magnetization", you should not specify
> starting_magnetization."

So, do you really want to fix the total magnetization of the system or 
do you want it to reach its ground state magnetization?


> from the pw.x input file description. If i
> still should specify the starting_magnetization?

If you are using the broadening of the occupations, I think you should. 
If you want to fix the total magnetization in this case you should use 
constrained_magnetization, not tot_magnetization method (which still 
might work, but probably will not be able to reach self-consistency).

> And If i want the
> amount of electronic magnetization determined during the self-consistent
> cycle, how should i specify the starting_magnetization?
>    

It dipends on your system. In many cases any reasonable value between -1 
and 1 is good. If you can guess a value close to that of the ground 
state then the code will reach self-consistency faster. In complicated 
systems you may get stuck in some local minimum if the 
starting_magnetization is too "wrong".

HTH

GS

> Thanks for your help!
>
> Weyl
>
> ===========================================================================
>
> Weyl FANG
> Graduate student in Chemical Engineering
> State Key Laboratory of Materials-oriented Chemical Engineering
> College of Chemistry and Chemical Engineering
> Nanjing University of Technology, 210009, Nanjing, Jiangsu, China
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> Email: weylfang at gmail.com
> Office: Room A705, Technical Innovation Building, Xinmofan Road 5#, Nanjing, Jiangsu, China
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-- 

Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne