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Convergence with respect to the number of plane waves can be rather slow,
and we recommend to test the calculations carefully.
Specifically, the calculations should be performed at the default energy cutoff ENCUT,
and at an increased cutoff (ideally the default energy cutoff
Another issue is that energy volume-curves are sometimes not particularly
smooth. In that case, the best strategy is to set
ENCUT = 1.3 times default cutoff energy
ENCUTGWSOFT = 0.5 times default cutoff energy
where the default cutoff energy is the usual cutoff energy (maximum ENMAX in POTCAR
The frequency integration also needs to be checked carefully, in particular for
small gap systems (some symmetry broken atoms) convergence can be rather slow, since
the one-electron band gap can be very small, requiring a very small minimum
in the frequency integration.
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