[Pw_forum] A bug in the pp.x?

[Axel Kohlmeyer]

On Sun, 8 Jun 2008, zhaohscas wrote:

HZ> >You are right: the actual check performed by the code is:
HZ> >  e_i \cdot \e_j > 1.d-6
HZ> >which wrongly allows non-orthogonal vectors if their pairwise scalar
HZ> >products are negative. Thank you for reporting, it will be fixed in the
HZ> >next release.
HZ> 

HZ> But, in my mind, as for the study of the distribution of the charge 
HZ> density, we generallly want to have the distribution w.r.t a 
HZ> specific miller plane.  In the periodic crystal system, this can be 
HZ> represented on the plane determined by a parallelogram whose two 
HZ> sides are the corresponding primitive plane vectors.  If we consider 
HZ> this requirement, I think we should use miller plane vectors to 
HZ> contruct the grid, which are not always perpendicular indeed.  
HZ> Under the above consideration, the orthogonal condition will be not 
HZ> so good.


that is all find and good, but the code actually has to be
able to do this. those checks have the purpose to stop people
from getting bogus output (and publishing them a _new_ science).

so before lifting one of those restrictions, one has to
validate that the code in question gives the correct results,
and - most likely - the missing parts will have to be implemented. 

there are essentially two major forces that drive open source
scientific software: 1) people that want to do something specific
and sit down and program it, 2) people that want a degree or a
salary or a professor position or ..., so they sit down and write
what their bosses/advisor/peers ask them to do.

unfortunately, there is a large difference between the number
of good and useful ideas and the people that fall under those
two categories, and on top of that for some strange reasion
they prefer to implement their own ideas (or those of their 
bosses/advisors/...) ;-)

cheers,
   axel.


HZ> 
HZ> Yours sincerely,
HZ> Hongsheng.
HZ> 
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-- 
=======================================================================
Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
   Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
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If you make something idiot-proof, the universe creates a better idiot.