Screened Columb matrix between KS basis

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Screened Columb matrix between KS basis

Postby damao4361556 » Sat Feb 10, 2018 4:36 pm

Dear YAMBO developers,

Recently I have initiated the topic of extraction of screened Columb matrix.
I would like to thank Daniele and Davide for their valuable comments.

Davide indicated that the BSE kernel containing only the screened Columb matrix can be stored in ndb.BS file if the number of G-vector in exchanges part equals to 0, according to the email communication with Davide.
there is also a way to output Screened Columb matrix by outputting the H_c of K.F file into txt format according to discussions with Daniele,

I understand that the Screened Columb matrix in YAMBO is between 2 excitons (eh pair) in YAMBO,
I would like to still ask the question is there a possibility to output the Columb matrix between just KS basis (e.g., 2 KS orbitals) in YAMBO, e.g., I will need to modify the code?
Sorry for many questions, just want to be for sure about this point? this is important since we want to further process the screened Columb matrix.

thanks for all your helps.

Wei Li
Institute of theoretical chemistry
Jilin University, PR China
Posts: 39
Joined: Wed Dec 16, 2015 8:11 pm

Re: Screened Columb matrix between KS basis

Postby Daniele Varsano » Sat Feb 10, 2018 5:37 pm

Dear Wei LI,
I understand that the Screened Columb matrix in YAMBO is between 2 excitons (eh pair) in YAMBO,

The W matrix elements are between eh pairs, which are not excitons, as the exciton will result as a linear combination of eh pairs after diagonalization of the excitonic matrix.
I'm afraid that what you ask is never calculated in Yambo as not entering in the BS equation. May you can be interested in diagonal matrix elements <phi_c phi_v | W | phi_c phi_v> ?
In this case you can extract them from the thread we had some days ago.

Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
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Daniele Varsano
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Re: Screened Columb matrix between KS basis

Postby Davide Sangalli » Mon Feb 12, 2018 1:21 pm

Dear Wei Li,
Danile already replied. Few more comments.
The screened elelctron-electron interaction is between two pairs of KS orbitals since the related operator in second quantization is a four point quantity, although it just depends on two spatial indexes.
As Daniele wrote, K.F gives you its expectation value between two eh-pairs <phi_ck phi_vk | W | phi_c'k' phi_v'k'>

Also please notice that ndb.BS is a binary file written with the netcdf library.
If you use ncdump (an executable provided with the netcdf library) you can inspect its content
ncdump ndb.BS > ndb.BS.dat
Pay attention that the result can easily be a huge file.

Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre
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