[gpaw-users] Functional specific convergence problem

[Lasse Vilhelmsen]

Hi,

I have a problem converging a system with the M06-L functional. The system causing the problem is a MgO(100) slab with an oxygen vacancy. The system converges without any problems if I have an adsorbate on the slab or if the vacancy isn't present. 

I have tried changing the following parameters:
- Spin polarisation
- Number of k-points
- Mixing (I've tried a lot of very conservative combinations)
- Eigensolver (I've tried them all)
- Translating the slab a bit in the cell
- Changing the size of the slab (both number of layers and the surface size)
- Different starting geometries (small displacements around the equilibrium structure)
- Different PBE starting densities (changing the convergence)
- Number of bands to converge
- Fermi temperature (0.0, 0.05, 0.1, 0.5)

The slab converges without any problem with both PBE and TPSS.

Attached is both a sample script which shows this problem and a log from running the script. As can be seen from the log the slab starts oscillating between two different energies and it seems like it can't decide on which minimum to choose.

I hope that some of you have a good suggestion or two for other parameters I can change to get the slab converged.

Best Regards
Lasse Vilhelmsen

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