[QE-users] 3d-rho resolution

[Giuseppe Mattioli]

Dear Aleksandra
If I understand well your question, you should change the FFT grid in  
the pw.x input rather than changing the pp.x input, using this:

    Variables:      nr1, nr2, nr3

    Type:           INTEGER
    Description:    Three-dimensional FFT mesh (hard grid) for charge
                    density (and scf potential). If not specified
                    the grid is calculated based on the cutoff for
                    charge density (see also "ecutrho")
                    Note: you must specify all three dimensions for  
this setting to
                    be used.

I verified in the past that the grid can affect properties (e.g.,  
Bader charges) calculated on .cube files generated by pp.x. As  
specified, default values for a given cutoff are reported in the  
output. This is for a calculation using NC PPs (ecutrho=4*ecutwfc=360  
Ry, ibrav=1, celldm(1)=40.0).

Dense  grid:  3093216 G-vectors     FFT dimensions: ( 240, 240, 240)

Be aware that larger FFT grids significantly affect the computational  
cost of the calculation.
HTH
Giuseppe

Quoting Aleksandra Oranskaia <aleksandra.oranskaia at kaust.edu.sa>:

> Dear users and developers,
>
> I am trying to generate more and less accurate electron density cubes (to
> study how some properties, extracted from cubes, depend on their
> resolution) but fail somewhere.
>
> Here is the pp.x input:
> &INPUTPP
> prefix = myinput
> filplot = myinput.rho
> plot_num = 0
> /
> &PLOT
> nfile = 1
> filepp(1) = myinput.rho
> iflag = 3
> output_format = 6
> !e1(1) = 1, e1(2) = 0, e1(3) = 0
> !e2(1) = 0, e2(2) = 1, e2(3) = 0
> !e3(1) = 0, e3(2) = 0, e3(3) = 1
> x0(1) = 0, x0(2) = 0, x0(3) = 0
> nx = 1000, ny = 1000, nz = 1000
> fileout = myinput.cube
> /
>
> Regardless of nx, ny, and nz (e.g. 50, 50, 50 vs 1000, 1000, 1000) I get
> the same outputs. What should I change to generate cubes with different
> resolutions? Parameters in SCF are very accurate, so my guess: It is pp.x
> input lines. not pw.x parameters.
>
> Thank you in advance!
> --
> Best wishes,
> Al., phd candidate in chemical sciences
> 'I.. a universe of atoms, an atom in the universe' (Richard P. Feynman)
> https://cpms.kaust.edu.sa/
>
> --
>
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GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>