The system is a metal but Drude term not included

Concerns issues with computing quasiparticle corrections to the DFT eigenvalues - i.e., the self-energy within the GW approximation (-g n), or considering the Hartree-Fock exchange only (-x)

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Dean
Posts: 98
Joined: Thu Oct 10, 2019 7:03 am

The system is a metal but Drude term not included

Post by Dean » Sun Dec 18, 2022 4:18 am

Dear Yambo developers and users,
I am doing GW calculation for 2D metal/half-metal materials. When I activate the Dude variables using the verbosity -V resp, but only infver appear in input file (I do not why).
So, I add DrudeWXd/DrudeWBS variables by hand in the input.
After running yambo, the out file reported "The system is a metal but Drude term not included".
By the way, when the new version of yambo enhancing the capability to treat metallic systems will be released?
Any help is appreciated.
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Dr. Yimin Ding
Soochow University, China.

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Daniele Varsano
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Re: The system is a metal but Drude term not included

Post by Daniele Varsano » Sun Dec 18, 2022 12:31 pm

Dear Yimin Ding,

this happens because the Drude model is meant for a full frequency calculations and you can activate it by:

Code: Select all

yambo -gw0 r -V resp 
anyway, this calculation is very cumbersome and if you want to stay with plasmon-pole approximations you can try to converge the calculation using many k points.
The new algorithms to treat metallic systems will be included in the next release of the code.

Maybe someone working on metals can provide you more advises.
Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

Dean
Posts: 98
Joined: Thu Oct 10, 2019 7:03 am

Re: The system is a metal but Drude term not included

Post by Dean » Mon Dec 19, 2022 7:59 am

Dear Daniele,

Thanks for your reply.
Drude term is included in my calculation in a test. The test is done.
But, I do not know how to set the values for Drude term, when my calculation is for a newly designed material theoretically.
Can you provide any tutorial or references on metals?

Thanks in advance.
Dr. Yimin Ding
Soochow University, China.

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Daniele Varsano
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Re: The system is a metal but Drude term not included

Post by Daniele Varsano » Mon Dec 19, 2022 8:24 am

Dear Dr. Yimin Ding,

the Drude is a model and needs empirical parameters from input. If they are not available, what you can do is to perform and RPA calculation at the smallest available q vectors,
identify the plasmon frequency and use it in the Drude model, i.e. approximate the q=0 plasmon peak with the one of the smallest available q.

Best,

Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

DarioALV
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Joined: Wed Dec 14, 2022 11:16 am

Re: The system is a metal but Drude term not included

Post by DarioALV » Mon Dec 19, 2022 11:51 am

Dear Dr. Yimin Ding,

As explained by Daniele, the Drude model in some versions of yambo has been looked when combined with PPA. I am not sure if it is available in the version you are using, however the variables you need to add in your GW/PPA input in order to check it are:

PPAPntXp
DrudeWXp

note the last character 'p' stands for PPA, while within the full frequency approach it is replaced by 'd'. You can ignore any possible warning and check if the inclusion of the Drude term has any effect in the GW quasiparticles.

Just to point out some features of GW calculations for metals in yambo, they need two contributions to the polarizability, coming from intra and inter-band transitions. In a standard calculation (e.g. without the inclusion of the Drude model), both contributions are computed for finite q, but in the limit q -> 0 only the inter-band term is numerically evaluated and the Drude model is a simple way to add the missing intra-band limit. There are two practical consequences: first, the effects of the intra-band limit are not always relevant, for example the contribution of the inter-band limit could be much more larger than the intra-band one and it can be ignored (inter+intra ~ inter), for instance this is the case of Al. Second, even when the intra-band limit is important, the results can be improved systematically by increasing the number of k-points, which results in the smaller finite q closer to q=0, of course, this convergence is cumbersome as mentioned by Daniele and is preferable to use other approaches like the Drude model in order to accelerate it.

So, I would suggest you trying to evaluate the importance of the intra-band limit in each of your systems. If the Drude model is not available with PPA, you can try it with the full frequency approach, as suggested by Daniele. This is a much more expensive method and there will be an efficient alternative, called the multipole approach (MPA), in new releases of yambo (https://link.aps.org/doi/10.1103/PhysRevB.104.115157). Fortunately, to test the effects of the intra-band limit there is not need to use converged GW parameters, you can set low fixed values for the energy cutoff and number of bands in the polarizability, and change only the number of k-points. The difference in the computed quasiparticles with and without the Drude model are more or less independent of the fixed parameters and can be use as an estimate of the error in your fully converged calculations.

Regarding the case of metals for which there is not an available Drude frequency, the intra-band limit can be numerically evaluated at the independent particle or the RPA level, as suggested by Daniele, for instance by integrating eq. 17 of https://link.aps.org/doi/10.1103/PhysRevB.64.195125. You can also read these other papers:
https://doi.org/10.1103/PhysRevB.77.035117
https://doi.org/10.1103/PhysRevB.82.035104
https://doi.org/10.1103/PhysRevB.86.035120

In the near future there may be other alternative approaches to address the intra-band limit in yambo. I can only comment on the ones I have worked on. There will be a dedicated paper for metals particularizing the MPA method for this kind of systems and proposing a new simple and general ab initio method to evaluate the intra-band limit.

I hope I have been somehow helpful.

Best regards,

Dr. Dario A. Leon
Norwegian University of Life Sciences

Dean
Posts: 98
Joined: Thu Oct 10, 2019 7:03 am

Re: The system is a metal but Drude term not included

Post by Dean » Tue Dec 20, 2022 8:04 am

Dear Dr. Dario A. Leon,

Thanks for your reply. I will read the papers.
Dr. Yimin Ding
Soochow University, China.

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