[Pw_forum] relax structure question

[Layla Martin-Samos]

Hi yelena, I do not know anything about elph, but usually calculations in
PBC  should not depend on the origin of the coordinate system. If you make
the calculation just shifting ALL the coordinates by the same amount (which
means that you just shift the origin of the coordinate system). Then the
calculations should be equivalent.

cheers

Layla


2014-03-12 15:09 GMT+01:00 yelena <yelena at ipb.ac.rs>:

> Is
> ATOMIC_POSITIONS {crystal}
>     -0.000054104  -0.000054104   0.002714087
>      0.666666666  -0.000054104   0.002714087
>      0.333387437   0.333387437   0.002714087
>      0.666666666   0.333387437   0.002714087
>     -0.000054104   0.666666666   0.002714087
>      0.333387437   0.666666666   0.002714087
>
> equivalent to:
>
>      0.999945896   0.999945896   0.002714087
>      1.666666666   0.999945896   0.002714087
>      1.333387437   1.333387437   0.002714087
>      1.666666666   1.333387437   0.002714087
>      0.999945896   1.666666666   0.002714087
>      1.333387437   1.666666666   0.002714087
>
> Should my K points and q points grid be shifted now, like
>
> K_POINTS AUTOMATIC
> 16 16 1   1 1 0
>
>
>
> Thank you all for always being helpful.
> Best,
> J.
>
> On 12 Mar 2014 13:01, yelena wrote:
> > Hello everyone!
> > I have kind a silly question but I can't figure it out. So I
> > apologize
> > in advance, if I'm asking stupid things.
> > I have structure I want to relax and then do electron-phonon
> > calculation. But after relaxation I get negative coordinates and that
> > (I
> > think cause) some really small negative frequencies in elph
> > files...and
> > that leads to NaN lambda and Tc after lambda.x I tried same
> > coordinates
> > but larger q grid and same thing happens. When I remove negative
> > signs
> > from coordinates manually, negative frequencies do not appear and I
> > get
> > lambda and Tc and everything is ok (but of course, that's not correct
> > way to do it)
> > So is there any trick I could do to fix this problem? how not to get
> > minus sign for coordinates when performing relax scf?
> > Best regards,
> > Jelena Pesic,
> > PhD Student, Center for Solid State Physics and New Materials,
> > IPB Serbia
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>
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