[QE-users] Some questions about regterg

[carlossiero siero]

Thank you Stefano, 

now it is very clear.  

Carlos    En lunes, 29 de julio de 2019 16:44:23 CEST, Stefano de Gironcoli <degironc at sissa.it> escribió:  
 
  
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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