[Pw_forum] relax question

[xu yuehua]

about why i use etot_conv_thr
as well as  force_conv_thr= 1.d-6 Ry
as usual,in vasp and castep software,about 1.d-4 ev is ok
why it is so different between these DFT software ?
i don not understand.
need your help



2007/7/13, Stefano de Gironcoli <degironc at sissa.it>:
>
> a tipical bond stiffness, if I recall correctly, is in the range of
> 0.1-1.0
> Ry/bohr^2 thus a threshold of 1.d-6 Ry/bohr in the force means that you
> are
> asking a numerical accuracy in your interatomic distances of the order of
> 1.d-5-1.d-6 bohr... are you sure you really need it ?
> best regards,
> stefano deGironcoli, SISSA & DEMOCRITOS
>
> Quoting xu yuehua <njuxuyuehua at gmail.com>:
>
> > hello all
> > i am doing relax.
> > in my inputfile,
> > i use Bohr> and the output is
> >    atom   1 type  1   force =     0.00000290    0.00000095   -0.00000364
> >      atom   2 type  1   force =     0.00000081   -0.00000108
> 0.00000033
> >      atom   3 type  1   force =    -0.00000435   -0.00000425   -
> 0.00000160
> >      atom   4 type  1   force =    - 0.00000312   -0.00000321   -
> 0.00000080
> >      atom   5 type  1   force =    -0.00000446   -0.00000036   -
> 0.00000273
> >      atom   6 type  1   force =    -0.00000048    0.00000230
> 0.00000112
> >      atom   7 type  1   force =     0.00000164    0.00000118
> 0.00000060
> >      atom   8 type  1   force =     0.00000131   -0.00000040
> 0.00000145
> >      atom   9 type  2   force =    -0.00000362    0.00000154   -
> 0.00000201
> >      atom  10 type  2   force =    - 0.00000029    0.00000191
> 0.00000302
> >      atom  11 type  2   force =     0.00000576   -0.00000134
> 0.00000194
> >      atom  12 type  2   force =     0.00000390    0.00000276
> 0.00000233
> >
> > Total force =     0.000015     Total SCF correction =     0.000054
> >      SCF correction compared to forces is too large, reduce conv_thr
> >
> >      The maximum number of steps has been reached.
> > my qustion is ,force at every atom is ok ,but why  the program asks to
> > reduce conv_thr
> > my conv_thr is not enough small ?
> > or my total relax step (50) is not adequate?
> > is there any principle about these parameter?
> > need your help
> > thanks a lot
> > --
> > Xu Yuehua
> > physics Department of Nanjing university
> > China
> >
>
>
>
>
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-- 
Xu Yuehua
physics Department of Nanjing university
China
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