Some problems about the grid point of pot.cube file in the EXTERNAL_POTENTIAL subsection

[Nico Holmberg]

Hi,

You need to supply a cube file that contains as many grid points as the 
grid that holds the real space electron density in your simulation system 
(depends on the PW_CUTOFF and cell size). You can check the size of this 
grid by turning on the print key FORCE_EVAL/PRINT/GRID_INFORMATION (see 
example below). When you print out a cube file, unless you explicitly 
specify otherwise, only every second value along each axis is printed out 
(keyword STRIDE). You need to take this into account when you supply a file 
for READ_FROM_CUBE, because as far as I understand no 
interpolation/extrapolation from tighter/looser grids is possible.

An example output is given below. In this case, the grid contains 350^3 
points at a planewave cutoff of 500 Ry. So to summarize, if your system 
contains 54 data points along each direction (at STRIDE 1), then you need 
to provide a cube with 54^3 grid points. You need a larger cube file with 
(2*54)^3 grid points if you printed out the cube file with STRIDE 2.

 PW_GRID| Information for grid 
number                                          1
 PW_GRID| Grid distributed over                                   192 
processors
 PW_GRID| Real space group dimensions                                   
192    1
 PW_GRID| the grid is 
blocked:                                                NO
 PW_GRID| Cutoff [a.u.]                                                    
250.0
 PW_GRID| spherical 
cutoff:                                                   NO
 PW_GRID|   Bounds   1           -175     174                
Points:         350
 PW_GRID|   Bounds   2           -175     174                
Points:         350
 PW_GRID|   Bounds   3           -175     174                
Points:         350
 PW_GRID| Volume element (a.u.^3)  0.2459E-02     Volume (a.u.^3)    
105442.7279
 PW_GRID| Grid span                                                    
FULLSPACE
 PW_GRID|   Distribution                         Average         
Max         Min
 PW_GRID|   G-Vectors                           223307.3      223650      
223300
 PW_GRID|   G-Rays                                 638.0         
639         638
 PW_GRID|   Real Space Points                   223307.3      245000      
122500

 RS_GRID| Information for grid 
number                                          1
 RS_GRID|   Bounds   1           -175     174                
Points:         350
 RS_GRID|   Bounds   2           -175     174                
Points:         350
 RS_GRID|   Bounds   3           -175     174                
Points:         350
 RS_GRID| Real space distribution over                                  4 
groups
 RS_GRID| Real space distribution along 
direction                              1
 RS_GRID| Border 
size                                                         29
 RS_GRID| Real space distribution over                                  6 
groups
 RS_GRID| Real space distribution along 
direction                              2
 RS_GRID| Border 
size                                                         29
 RS_GRID| Real space distribution over                                  8 
groups
 RS_GRID| Real space distribution along 
direction                              3
 RS_GRID| Border 
size                                                         29
 RS_GRID|   Distribution                         Average         
Max         Min
 RS_GRID|   Planes                                 145.5         
146         145
 RS_GRID|   Distribution                         Average         
Max         Min
 RS_GRID|   Planes                                 116.3         
117         116
 RS_GRID|   Distribution                         Average         
Max         Min
 RS_GRID|   Planes                                 101.8         
102         101

BR, 

Nico


perjantai 1. joulukuuta 2017 11.19.13 UTC+2 jts2... at gmail.com kirjoitti:
>
> Hi everyone,
>
> I have asked several questions about the same subject. Until yesterday, I 
> have figured out the meaning of the *.cube file generated by CP2K. 
> What I want to do is to add potential to my simulation system, but the 
> potential is calculated from Poisson equation using finite element method.
> Hence I only have grid point values of the potential. 
>
> So the solution is adding the potential from pot.cube file using 
> READ_FROM_CUBE option. I will try this in a simple simulation to figure the 
> structure. 
> The simulation box in my simulation is a cube, whose length of a side is 
> 12.4138 (Angstrom, I think). And from the *.cube file I know the length 
> of the 
> vector along x, y and z direction is 0.434420(Angstrom, maybe). What's 
> more, the number of data points along each direction is 54.
>
> Now I need to supply the pot.cube file to CP2K. I wonder how many grid 
> point value should be given?
> (54*12.4138 / 0.434420) ^3 ?
>
> I major in mathematic, so the easy thing for you may be a problem for me.
>
> Thanks for your reply !
>

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