Yambo Community Forum

Dear all:

When I judge the convergence of k-mesh by calculating the spectrum, I use different k point densities from 12*12*1 to 24*24*1 for two-dimensional materials with lattice constant of 3.55 angms. For the first absorption peak, I can always see the tiny displacement of the absorption peak in energy, when k=12, the highest peak is 1.88eV,
k=12, ~1.88eV.
k=14, ~1.98eV.
k=16, ~2.06eV.
k=18, ~2.10eV.
k=20, ~2.16eV.
k=24, ~2.22eV.
Although the energy position of the first absorption peak is biased, it is consistent with the light absorption intensity. Does it look like we still haven't reached the point k of convergence? I appreciate any guidance and tutorial on that!
Best,
sunxl

Dear sunxl,

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Yes, it seems that convergence is very slow. My advice is to increase the grid point uniformly in terms of k spacing, ie Nkx and Nky proportional to the unit cell lengths.

Best,
Daniele

Dear Daniele:

Thank you for your advice. For my material lattice parameter of a=b=3.55 angstroms, do you mean that I should continue to increase k points until convergence?

Dear sunxl,

in this case your sampling is uniform, and you will need to increase the sampling if you aim at a tighter convergence.
Best,
Daniele