Possible tests and known issues

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 $\times 1.3$). 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 files). 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 $\omega$ in the frequency integration.