Hello Lorenzo, It's really nice to hear from you. I hope you're doing well.
So I am using QE 6.4 and unfortunately I can see that the scf calculation takes same amount of time as the band calculation. So I doubt that the problem might be the inconsistency between these two calculations. But sure, I'll increase the ecutwfc. Thank you for the tip. Aslo I have tried running the band calculation on different systems (local pc with 12 nodes) and HPC (with 36 and 72 nodes). Every time I have the same problem. I have tried QE 6.5 and 6.4 for this calculation all with same issue. All the best, Zahra On Fri, Dec 11, 2020, 22:22 Lorenzo Paulatto <[email protected]> wrote: > 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 > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list > [email protected]https://lists.quantum-espresso.org/mailman/listinfo/users > > _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users
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