[Pw_forum] calculating band derivative by wave functions

[Chong Wang]

Hello,


I am trying to read wave functions from pw_export.x output. To check whether I have done it correctly, I calculated <\psi_n|P|\psi_n>(P is momentum operator and is -i\hbar\partial_r) using fourier coefficients of wave functions, which should be proportional to band derivative. However, it turns out this is not the case. Now there are two possibilities:


1. Is it because I made some mistakes while reading wave functions? I think pw_export.x stores fourier coefficients of wave functions in 'Eigenvectors' tag and fourier components are stored in 'Wfc_grids'.


2. Is <\psi_n|P|\psi_n> not proportional to band derivative using pseudopotentials?



calculation details:


I am using norm conserving pseudopotential with PBE xc functional.



Best!


Chong Wang

Ph.D. candidate

Institute for Advanced Study, Tsinghua University, Beijing, 100084
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