[Pw_forum] question

Axel Kohlmeyer akohlmey at cmm.chem.upenn.edu
Thu Nov 23 22:33:52 CET 2006

On Thu, 23 Nov 2006, wang yanchao wrote:

WY> Dear users:
WY>    when I used run_pp to caculate the densety of charge,I found a qustion
WY> that the number of points are 55 55 55 in output file.but in fact what I
WY> input the nx,ny,nz is100,100,100.then  I read the code of PP,I found that 55
WY> 55 55 is nr1+1 nr2+1 nr3+1.I think "nr" is the K_point.In fact I

nr1,nr2,nr3 (and its siblings nr1s,nr2s,nr3s and nr1b,nr2b,nr3b) are
traditionally the grid dimensions of the real space meshes on which 
the density is stored (e.g. for evaluating the functionals or 
computing forces). see, e.g., Modules/input_parameters.f90
this is independent of your k-point selection.

WY> ,however,caculated the K_point is gamma.This make me confused.In an addtion
WY> ,I found the value of nx,ny nz is limited in code of PP.the max value is
WY> 64.I do not know the reson why it choose this value.If you know ,please tell
WY> me .Thank you in advance.

unless you need a specific real space resolution, you should stick
with the grid dimensions used in your pw.x calculations. for tighter
(or coarser) grids the code interpolates via fourier transforms
(as the real space density is usually generated from the g-space 
representation when needed).

hope that helps,


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
If you make something idiot-proof, the universe creates a better idiot.

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