[Pw_forum] question about FFT standard set by Quantum Espresso

Yu,Yue yuyue1995 at ufl.edu
Tue Jul 26 18:54:12 CEST 2016

Dear all,

I encountered a problem when trying add a extra term rho_extra(G) into hartree energy calculation (which is done by subroutine v_h in PW/src/v_of_rho.f90). Here rho(G) means density of charge in G space, which is generated from rho(r) by doing FFT.

Thus, I need to transfer my known rho_extra(r) (extra charge distribution needed) to corresponding rho(G) by doing FFT with hand, the problem is, I have no idea with the standard of FFT set by Quantum Espresso.
It is important to find how to properly get the rho(G) from rho(r) in the same way as QE do.

For example, how does  Quantum Espresso set the normalization factor for FFT in a supercelll with  volume=V? (It could be put into rho (G) as 1/V,  or into rho(r) as 1/V, or into both rho(g) and rho(r) as 1/sqrt(V)).

I will appreciate if you can offer any help.

Thanks a lot !

Yue Yu

Yue Yu
Ph. D student
Department of Physics, University of Florida

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