MPA in 2D systems: BZ sampling?
Posted: Wed Mar 25, 2026 12:00 am
Dear all!
When trying to use the MPA with 2D systems (MoS2 monolayer in this case), I encounter the following behavior (gap and VBM/CBM at the Gamma point!):
Convergence w.r.t. the BZ sampling within the Godby-Needs PPM:
kpt bnd_x bnd_g cutoff (Ry) gap vbm cbm
6x6x1 200 200 4 3.91217 -0.87991 3.03226
12x12x1 200 200 4 3.88638 -0.83605 3.05033
Using the RIM and RIM-W parameters for 2D systems, the QP energies are already converged (to within 50 meV here) with a 12x12x1 k-mesh, as it should be. Now the same thing for MPA with 'ETStpsXm = 8' (converged vs. 16 poles):
kpt bnd_x bnd_g cutoff (Ry) gap vbm cbm
6x6x1 600 600 16 5.12461 -1.82519 3.29942
6x6x1 200 200 4 5.20877 -1.37231 3.83646
12x12x1 200 200 4 4.37506 -0.96955 3.40551
24x24x1 200 200 4 3.98923 -0.79276 3.19647
48x48x1 200 200 4 3.82818 -0.66470 3.16348
The first line, in comparison to the second line, shows the convergence w.r.t. the bands (both for X and G) and the cutoff, both using a 6x6x1 k-mesh.
What am I doing wrong here? Why is the convergence w.r.t. the k-mesh much slower in this case? Is there something else to consider for the MPA in 2D systems? I attach the QE and Yambo input files, as well as the respective report files to this post.
Thanks for your explanations!
Christian
When trying to use the MPA with 2D systems (MoS2 monolayer in this case), I encounter the following behavior (gap and VBM/CBM at the Gamma point!):
Convergence w.r.t. the BZ sampling within the Godby-Needs PPM:
kpt bnd_x bnd_g cutoff (Ry) gap vbm cbm
6x6x1 200 200 4 3.91217 -0.87991 3.03226
12x12x1 200 200 4 3.88638 -0.83605 3.05033
Using the RIM and RIM-W parameters for 2D systems, the QP energies are already converged (to within 50 meV here) with a 12x12x1 k-mesh, as it should be. Now the same thing for MPA with 'ETStpsXm = 8' (converged vs. 16 poles):
kpt bnd_x bnd_g cutoff (Ry) gap vbm cbm
6x6x1 600 600 16 5.12461 -1.82519 3.29942
6x6x1 200 200 4 5.20877 -1.37231 3.83646
12x12x1 200 200 4 4.37506 -0.96955 3.40551
24x24x1 200 200 4 3.98923 -0.79276 3.19647
48x48x1 200 200 4 3.82818 -0.66470 3.16348
The first line, in comparison to the second line, shows the convergence w.r.t. the bands (both for X and G) and the cutoff, both using a 6x6x1 k-mesh.
What am I doing wrong here? Why is the convergence w.r.t. the k-mesh much slower in this case? Is there something else to consider for the MPA in 2D systems? I attach the QE and Yambo input files, as well as the respective report files to this post.
Thanks for your explanations!
Christian