[QE-users] vloc_of_g , a deep understanding

[Elena Cannuccia]

Dear all,

I am interested in understanding the calculation of pseudopotential in
plane waves. I have started from the subroutine vloc_of_g.f90.

I am aware of the fact that a separation of the short and long range part
of the Coulomb potential is obtained by means of the error function, and
the subsequent treatment of the two parts in order to get the Fourier
transform of the Coulomb potential.

I do not understand the multiplication by r(ir) at line 103
aux1 (ir) =r (ir) * vloc_at (ir) + zp * e2 * erf (r (ir))
and why, a few lines below, the Fourier transform is obtained by
sin (gx * r (ir) ) / gx .  Is it because the function to be transformed is
odd?

Some references will be really appreciated.
Thank you very much

Elena Cannuccia
Aix Marseille Université
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