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hi,
I am trying to optimize crystal structure of a monoclinic oxide. While the a, b, c, and the angle do not vary as I increase the cutoff energy from 400 to 500 and lastly to 550, or when I use more dense k-points, the total energy changes (goes down) by 0.1eV when using these more stringent parameters. Should I expect the total energy to converge at some point (for some high cutoff E and k-points)? Is that where I get the optimized lattice parameters?
Thanks.

Hi apple,

the short answers are: a) yes and b) yes.
However, if you change your ENCUT by only 20% do not expect too much change. Double it. Then you'll see, if the first set-up was ok.
Do you use O or O_s PAW? In case of O the cut-off is too small anyway (Pulay stress ...).
Have you wondered about raising total energy with higher cut-off energies? There is some compensation built in ('kinetic energy error for atom') ...

Hth

alex

Thanks Alex. I will play with the Ecutoffs.