[Pw_forum] Time of phonon calculation

[Gabriele Sclauzero]

Il giorno 15/mag/09, alle ore 16:29, 程迎春 ha scritto:

>
>
>
> &electrons
> /
> In the scf calculation, the default convergence threshold for scf  
> conv_thr is 1.D-6, but in the phonon calculation, the threshold
>  tr2_ph=1.0d-12,
> is much tighter !!!

Actually the converge thresholds for pw.x (conv_thr) and ph.x (tr2_ph)  
are not referred to the same quantity. The first is about the  
estimated error on the total energy, while the second is a sort of  
norm of the difference between the scf potential at two consecutive  
steps of the scf cycle (though I'm not completely sure).

>
> I think you can increase the scf threshold and decrease the phonon  
> threshold.  You can change the both threshold to 1.D-8.


In order to get good phonons it is usually better to have a well  
converged scf potential, so that it is good advice to decrease  
conv_thr down to 1.d-8.
However, to my knowledge, it is better not to increase tr2_ph with  
respect to the default (1.d-12).

GS

>
>
> -- 
> Y. C. Cheng
> Department of Physics
> Nanjing University
> Nanjing 210093
> P. R. China
> Tel: 86-25-83592907
> Email: yccheng.nju at gmail.com
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Gabriele Sclauzero, PhD Student
   SISSA & CNR-INFM Democritos,
   via Beirut 2-4, 34014 Trieste (Italy)
   email: sclauzer at sissa.it
   phone: +39 040 3787 511
   skype: gurlonotturno




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