[QE-users] query on number of k points in nscf

[Giovanni Cantele]

Dear all,

I’ve experienced a “strange” (?) behaviour in an NSCF calculation. I’m using Quantum-ESPRESSO v. 6.4 on CINECA-Marconi.

The calculation is with no symmetry ("No symmetry found”) and lists 19 k-points at the beginning of the calculation.
In the input the k-point specification is obtained through
K_POINTS { automatic }
36  1  1   0 0 0 

If I
grep "k =.*bands " NSCF.out | wc
19 lines are correctly found in the output.
However
grep "Computing" NSCF.out 
returns
     Computing kpt #:     1
     Computing kpt #:     2
     Computing kpt #:     3
     Computing kpt #:     4
     Computing kpt #:     5
     Computing kpt #:     6
     Computing kpt #:     7
     Computing kpt #:     8
     Computing kpt #:     
     Computing kpt #:    10
as if only 10 k-points were considered in the calculation. Even more strangely, by analizing the cpu-time information, I get
     Computing kpt #:     1
     c_bands: 56 eigenvalues not converged
     total cpu time spent up to now is    13728.9 secs
[….]
     Computing kpt #:    10
     c_bands: 48 eigenvalues not converged
     total cpu time spent up to now is   133710.2 secs

that is, the time for 10 k-points, is about 10 times that for a single k-point. However, the full calculation takes
     PWSCF        :   1d13h59m CPU   1d15h18m WALL
about 1d and 13 hours, that is 37 hours that correspond to about 133000 seconds. So it seems that the whole calculation
takes the same time as taken for the first 10 k-points.

So, the questions are:

1) why only 10 “Computing ….” lines are printed in output?
2) How can I be sure that the code effectively computed the k-points from 11 to 19 (and if it did not do it, what are
the eigenvalues printed at the and of the output for those k-points)?


Maybe I’m missing something very trivial (in the case I apologise for that!), but I cannot figure out what!

I also checked PW/src/c_bands.f90 and it seems that the line 
 IF ( iverbosity > 0 ) WRITE( stdout, 9001 ) ik
is within the loop
k_loop: DO ik = ik_+1, nks
so the printing of the message with format
9001 FORMAT(/'     Computing kpt #: ',I5 )
should occur for either all k-points or none of them.

I thank you in advance for any suggestion.

Giovanni


-- 

Giovanni Cantele, PhD

CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy

e-mail: giovanni.cantele at spin.cnr.it
            gcantele at gmail.com
Phone: +39 081 676910
Skype contact: giocan74
Web page: https://sites.google.com/view/giovanni-cantele

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