[Pw_forum] About the spline interpolation for charge density.

[Paolo Giannozzi]

On Jun 18, 2008, at 17:48 , zhaohscas wrote:

> I have the following 18*18*18 charge dentity datagrid as follows:
>
> ------------------------
>          a       b       c       Charge
>        1       1       1       0.430034694385803
>        2       1       1       0.433590624875083
>        3       1       1       0.444263507693938
>        4       1       1       0.461808085757678
>        5       1       1       0.485486354576373
>        6       1       1       0.514303497336158
>       ...     ...      ...
>        18    18       18
> ------------------------
>
> Where, the a, b, and c is FFT grid point used for sample the  
> charge, and the last column is the corresponding charge density at  
> the FFT grid point defined by crystal vectors: (a,b,c).
>
> I want to make a  spline interpolation to this datagrid to get a  
> more dense and smooth charge density datagrid,  I think this should  
> be done by spline interpolation.
>
> I've read the the source plotrho.f90 of pp.x, and can't figure it  
> out how can I make my issue solved.

plotrho.f90 performs simple linear interpolation. You may have a look  
at code
voronoy.f90: it performs a Fourier interpolation, i.e. transforms to  
real to
reciprocal space, pads additional Fourier components with zero,  
transforms
back to real space onto a denser grid.

Paolo
---
Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222