[QE-users] Convergence tests for slabs

[Léon Luntadila Lufungula]

Hi Giovanni,

Thank you for your answer! I do have some follow-up questions if you don't mind.

When converging the clean slab, which electronic properties do you propose to look at for convergence? Because up until now, I have only done convergence tests by looking at the total energies of my system... I come from molecular calculations, so I'm still a bit unfamiliar with things like the density of states and band structures. I'm mainly concerned about adsorption energies and analyzing the bonds inside the system by looking at the electron density and its derivatives (i.e. theories like QTAIM, ELF, NCI).

You also say that I should increase my unit cell size in the direction perpendicular to the slab, but can you just change just change your unit cell without consequences? I have been told that all your calculations have to be done in the same unit cell to be able to compare the values of properties such as the adsorption energy... Wouldn't changing the unit cell also change the plane wave basis set (i.e. larger unit cell = denser reciprocal lattice = more plane waves for a similar cutoff)?

For the dipole correction, I currently use the assume_isolated = '2D' flag enabled, while freezing the atoms in the bottom row of my slab to their bulk positions to simulate the bulk.

Kind regards,
Léon Luntadila Lufungula
Structural Chemistry group
University of Antwerp
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