[QE-users] Eigenvalues for vc relax not converging

Priya Shrivastava priyashrivastava16 at gmail.com
Fri May 11 08:35:18 CEST 2018

> >Dear Priya,
> >
> >Some quick comments:
> >
> > - Are you sure that the ecutwfc = 20 Ry is sufficient? The 40 Ry that
> you
> >mention sounds much more realistic, if not even higher value would be
> >needed; the calculation of the stress tensor ("vc-relax") requires a
> >stricter convergence with respect to the cut-off energy/basis set than
> for
> >example total energy as the former is a (second) derivative of the
> latter,
> >and the basis set would in principle be a function of the lattice
> >constant, so better be well converged in the basis set
>     Yes Sir,  I have changed it to 40 Ry.

  > - Since you have an FCC lattice you could easily calculate the total
> >energy of the ("relax"'ed) system as a function of the lattice parametre
> >and check if you converge toward the same value as the 'vc-relax'

   Thankyou for the suggestion but if i understand correctly did you mean
that i run 'relax' calculation instead of vc-relax?  and Also how does FCC
lattice makes a difference to
   calculation of total energy (did you mean symmetry-wise?)

>   - Do I understand you correctly that you can reach convergence in the
> self-consistent loop, but in the subsequent loops the electronic structure
> does not convergence (as the D3 does not affect the electronic structure
> explicitly, only via the modified lattice constant)

  Yeah it seems so to me. Please see the ouput (see link)---->.

 - Your value for smearing is quite small; you could at least temporarily
try to increase it

   I have made it 0.01 (job is running). i will send the ouput once it is

>   - What is the lowest value of convergence that you reach in, say 100
> iterations?
>     Please see o/p (see link) for better insight. Thank you Dr. Apsi for
your kind comments.

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