Hello Zahra,
if I understand correctly, you manage to do the scf calculation, but
then the band calculation is very slow. The cost per k-point of nscf
should be more or less the same as the cost per k-point of one scf
iteration. If it is not, there is something wrong. One possible problem,
is that ecutwfc is interpreted differently during nscf. A tight value
(1.d-12 or less) may cause the threshold of diagonalization in nscf to
become too small and very slow to converge. This should be fixed in v
6.7, but you can just increase ecutwfc in nscf if you're using a
previous version.
If not, it may be a problem with parallelism, i.e. running on too many
CPUs or some proper human error like running with all the processes on
the same computing node.
cheers
On 2020-12-11 19:25, Zahra Khatibi wrote:
Dear all,
First of all, I hope everyone is safe and well in these crazy times.
I'm calculating the electronic band dispersion of a 2D heterostructure
with a 59 atom unit cell. This system is a small bandgap (10-20 meV)
semiconductor. The number of valence bands is (valence electrons/2)
181. When I set 'nbnd' to 190, the band structure calculation costs me
30 minutes for each k point on HPC with 72 processors. This means that
if I do a simple band calculation for a high symmetry path with 100
points within, I have to wait almost 50 hours! This even becomes worst
when I try to evaluate the band dispersion with SOC switched on (twice
the spin degenerate band calculation).
Since the band dispersion evaluation is the major part of our study, I
was wondering if there is a way around this problem, like reducing the
number of bands by only looking at energy interval close to Fermi energy?
I could see that there are lots of papers and studies in the
literature with huge unit cells and heavy atoms that have
presented numerous band structures (using QE). So I really appreciate
it if you could help me here.
Kind regards,
--
Z. Khatibi
School of Physics
Trinity College Dublin
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Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
users mailing list [email protected]
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