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

[Lorenzo Paulatto]

Dear Giovanni,
if you are using pools, only a fraction of the k-points will be 
enumerated in the NSCF calculation.
kind regards

On 08/04/2019 12:07, Giovanni Cantele wrote:
> 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 <mailto:giovanni.cantele at spin.cnr.it>
> gcantele at gmail.com <mailto:gcantele at gmail.com>
> Phone: +39 081 676910
> Skype contact: giocan74
> Web page:https://sites.google.com/view/giovanni-cantele
> 
> 
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-- 
Lorenzo Paulatto - Paris