Dealing with large unit cell

Dear all,

I am working on a material system with a large unit cell (84 atoms, over 2000 ų in volume). The material is chemically disordered, and I’m trying to find the ground state configuration.

To make the structure as close to cubic as possible, I have constructed a 1x1x2 supercell. This results in over 6e8 possible configurations.

Even with relatively small cut-off radii of [8.0, 6.0] for the cluster space, I still end up with 1450 parameters in the expansion. Unfortunately, due to limited computational resources, I can only afford to run DFT on ~200 structures, but the annealing procedure suggests that this is too few for a reliable cluster expansion model.

Is there any strategies that can solve this situation?

Best regards,
Zane

Hi,
If you can only afford 200 DFT calculations, then I’d suggest to reduce the cutoffs (maybe discard triplets?) such that you end up with maximum around 100 parameters.

Then its always a good idea to try to converge the choice of cutoff wrt to e.g. the cross-validation error.

Dear erikfransson,

Thank you very much for your suggestions.

I will give it a try.

Best regards,
Zane