# Is Wannier 90 computationally expensive to run?

I'm extremely new to the Wannier90 code. I was planning to install it on a workstation I have but I would be using the cores to run calculations using Quantum ESPRESSO.

I have a few quad core i5 PC's. So would installing the wannier90 code on those be a good move? I'm mostly working with primitive unit cells which would have at most 10 atoms.

• The cost should still scale cubically with supercell size, same as the pw.x code on Quantum ESPRESSO. So, if you can perform DFT calculations without much difficulty, wannier90 should be fine as well. Feb 12, 2021 at 0:51
• @Xivi76 Thank you!! So its like a single iteration calculation?
– Atom
Feb 12, 2021 at 7:59
• @Atom You can set the interation number in the wannier90 input file.
– Jack
Feb 15, 2021 at 3:17
• @Xivi76 why don't you turn that into an answer? We could really use some shortening of the unanswered queue which is getting quite big lately. Feb 19, 2021 at 16:37

## 1 Answer

Wannier90 should still scale cubically with size of the supercell, same as pw.x on Quantum ESPRESSO. Regarding the number of iterations needed, it depends on your system. Assuming you are generating MLWFs (Maximally Localized Wannier Functions) first, the number of iterations required to converge depends on the parameters in your system, like K-Points. Look at Table 1 in this document [2] for an idea of the relative time-scales for the wannier procedure for bulk silicon. You control the number of iterations using the num_iter tag. But as you might imagine, you can't set this tag to an arbitrarily low value. The correct method should be to set this to a high enough number so that the amount of spread '$$\Omega$$' in k-space is low. This is indicated by the Im/Re ratio printed in the output.

References:

1. Mostofi, Arash A., et al. "wannier90: A tool for obtaining maximally-localised Wannier functions." Computer physics communications 178.9 (2008): 685-699.
2. https://arxiv.org/pdf/0708.0650.pdf