Yambo Community Forum

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

Dear Christian,

I agree this is indeed strange.
Could you please tell us what version of Yambo you are using? I cannot find the report file of the MPA and PPA calculations (these also could be useful)

Thanks

Best,
Giacomo

Hi Giacomo!

Here are the report files. As you can see, I am using version 5.3.

Thanks,
Christian

Hello Christian,

so looking at your reports, it seems the RIM-W procedure it is not activated at all for the mpa calculation, this explains the very slow convergence.
This is a small annoying bug that I thought it was solved, but apparently it is still present in yambo 5.3.

I would suggest, if possible, to switch to yambo 5.4, there mpa+rim_w is working correctly.
By the way, in your input I would also add the line rimw_type='semiconductor'. This is not strictly necessary in yambo 5.4 as this is the default, however the rimw_interpolation is customed also for other cases (2D Dirac bands, metal).

Best,
Giacomo

Dear all,
I am trying to implement MPA for GW calculation in a 2D system. Can someone please provide me the right fully command to generate correct input file for the same?
It'll be really helpful.

Thank you

Dear Nilesh,

to generate an input file for a GW mpa calculation of a 2D system, I would proceed as follows:
note that the m stands for mpa. The -r flag activates the calculation of the RIM Coulomb potential and allows to set a cutoff.
The -r flag instead activates the RIM-W procedure, in case you need it.

Best,
Giacomo

Dr. Sesti,
Thank you for your kind reply and the command to generate input file. It's really helpful.
I have another stupid question, how to converge these quantity on Hartree-Fock level in case of metals (when i run HF part, i got band gap 'NaN').
EXXRLvcs= 152857 RL # [XX] Exchange RL components
VXCRLvcs= 152857 RL # [XC] XCpotential RL components


I am just following standard procedure as semiconductor for metals too. So, please guide me in this direction too.

Thank you

Dear Nilesh,

In case you want to converge EXXRLvcs and VXCRLvcs for a metal, I would consider energy differences between occupied and unoccupied states. I would expect the band gap reported by Yambo to be null as it is dealing with a metal.
Nevertheless, also using the maximum value of EXXRLvcs and VXCRLvcs should not be a problem, unless you have computational limitations.

Best,
Giacomo

Dear Nilesh,

you have a NaN it is possible there is some miscompilation/linking of the linear algebra libraries, you can try to use the internal linear algebra using "--enable-int-linalg" option in the configure script and see if this solves the problem.

Best,
Daniele