[CP2K:4359] possible bug in Ewald routine ?

[vish]

Dear Dr. Hutter,

Thanks for the reply.

Best,
Vishal

On Tuesday, March 26, 2013 1:30:21 AM UTC-7, jgh wrote:
>
> Hi 
>
> the input to the EWALD routines is for historical reasons 
> rather complicated. There are three parameters that define 
> an Ewald calculation: 
> - alpha (width of the Gaussian compensation charge) 
> - the real space cutoff (equal to the cutoff of nonbonded forces in CP2K!) 
> - the reciprocal space cutoff 
>
> Given a desired accuracy and anyone of the above three parameters 
> determines the possible range of the other two parameters. 
> However, in CP2K you have to define all three parameters independently 
> in the input. In addition, the reciprocal cutoff is given by 
> the number of grid points, this means depends on the box size! 
>
> And finally, the regression tests are not 'real' inputs. You 
> cannot rely on the parameters used there to give you converged 
> results. You have to find them yourself. 
>
> regards 
>
> Juerg Hutter 
>
> -------------------------------------------------------------- 
> Juerg Hutter                         Phone : ++41 44 635 4491 
> Physical Chemistry Institute   FAX   : ++41 44 635 6838 
> University of Zurich               E-mail:  hut... at pci.uzh.ch<javascript:> 
> Winterthurerstrasse 190 
> CH-8057 Zurich, Switzerland 
> --------------------------------------------------------------- 
>
> -----cp... at googlegroups.com <javascript:> wrote: ----- 
> To: cp... at googlegroups.com <javascript:> 
> From: vish 
> Sent by: cp... at googlegroups.com <javascript:> 
> Date: 03/26/2013 01:17AM 
> Subject: [CP2K:4359] possible bug in Ewald routine ? 
>
> Dear CP2K users, 
>
> EWALD section requires one to input ALPHA (ang -1) parameter. In general, 
> I would expect changing this value should not have any affect on the total 
> potential energy of the system. However, when I change ALPHA in the tests 
> files in CP2K tests files, the total potential energy changes a lot (for 
> example water512.inp in tests/Fist folder). I was wondering if there is a 
> bug in ewald routine or I am understanding this wrongly? 
>
> Any help on this is greatly appreciated.  
>
> Thanks in advance, 
> Vishal   
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