# [Pw_forum] hard and smooth reciprocal space grid

Jacopo Simoni simonij at tcd.ie
Tue Oct 3 02:26:35 CEST 2017

Dear PWSCF users,

I am trying to understand the difference between hard and smooth grid, in
particular I would like to reconstruct the real space density that you
obtain in output from pp.x starting from the real space wave functions that
I have obtained from wfck2r.x

It seems to me that you cannot do this straightforwardly by simply
computing sum_ibnd sum_k W_k |\psi_ibnd,k(r)|^2
I understand that the reason is that the wave function cut-off is much
smaller than ecutrho that by default is 4 times bigger.

Could somebody explain to me, first, if this computation is possible by
using the data in wfck2r and secondly how can I do this (or even which
routine should I look at) ?

I really appreciate any help. Many thanks in advance.

Jacopo Simoni
Los Alamos National Laboratory, Theoretical Division
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