[QE-users] Some questions about regterg

[Stefano de Gironcoli]

g_psi multiplies the correction vector by an approximation of the 
inverse of (H-eS), typically just the inverse of the diagonal .

regterg is the real version of the routine: that is appropriate the one 
for k==Gamma

in this case psi is real in real space which means that the Fourier 
components at G and -G are complex conjugate of each other.

the normalization is as usual

1 = \sum_G psi(G)^* psi(G)   when summing over all G

but only half of them (the "positive" G) are stored and the 
normalization is computed as

1 = psi(0)* psi(0) + 2.0 \sum_G/=0 psi(G)* psi(G)   or rather

1 = 2.0 \sum_G psi(G)* psi(G)   -  psi(0)* psi(0)

the processor with gstart==2 is the one for which the first component is G=0

HTH

stefano

On 29/07/19 15:59, carlossiero siero wrote:
> Dear Users,
>
> I have been digging in the regterg.f90 subroutine and I was wondering 
> if somebody could tell me what the calling to g_psi (line 286) is doing?
>
>                 |     CALL g_psi( npwx, npw, notcnv, 1, psi(1,nb1), 
> ew(nb1) )
>
> I thought the correction vectors, |psi> = (H - e*S) |psi>, were 
> already stored in psi, so there is no need to do any inversion or 
> anything else.
>
> Also, running a 1processor calculation, the normalization goes through 
> line 299:
>
>                 |      IF ( gstart == 2 ) ew(n) = ew(n) - psi(1,nbn) * 
> psi(1,nbn)
>
> What is the purpose of substrating the psi product of the first 
> element on each of the new vectors?
>
> Thanks so much for your help!
>
> Carlos
>
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