[CP2K:2239] Re: handling periodic images

Teodoro Laino teodor... at gmail.com
Sat Aug 22 03:05:04 CEST 2009


Noam Bernstein wrote:
> Hi Teo - thanks for the quick response.  The bottom line is that you're right
> about CENTER_COORDINATES.  Removing that fixed the problem.  I didn't
>   
you're welcome
> I don't really understand the behavior, though.  The problem happens when
> you move an extremal atom, and the CENTER_COORDINATES stuff
> translates your entire molecule.  But how come it's sensitive to that, but not
> to displacements of atoms that are deeper in the molecule?  Is it just
>   
if you translate all the atoms by a small dr the forces will be 
different as well from the non-translated one.
XC is severely modulated by the grid spacing in all PW-codes (of course 
doing DFT).
This problem can be cured in few ways but this does not mean that it 
does not exist.
> that if the whole system is translated, every atom moves a little bit, and
> the errors add up?
>
> I also disagree about PW codes not being translationally invariant.
> Plane waves are translationally invariant by construction.  But pretty much
>   
well depends what si the meaning for you of "some stuff". Maybe  XC (see 
above)? 
Check in the literature for the "ripples" modulation of the PES in a 
PW-code.

Teo

> all real codes do some stuff on a real space grid, and that breaks
> translation invariance.
>
> In any case, problem solved.
>
>                           Noam
>
> >
>   




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