Yambo Community Forum

Dear sir,
I have a question about the calculation of the band structure of monolayer MoS2. As I am not familiar with YAMBO and some theories, I wonder if I can follow the example of hBN (How to obtain the quasi-particle band structure of a bulk material: h-BN) to calculate the energy band structure of monolayer MoS2. I saw another tutorial on "How to treat low dimensional systems", which means i have to add truncation of the Coulomb potential for 2D systems. But I don't know when the cutoff coulomb potential needs to be added, and how it fits into the example of the hBN band structure.
Another problem is when I follow the example "How to analyse excitons" and run ypp -J 2D_WR_WC -e s 1, I get an error and I don't know how to fix it.The error is shown below:
forrtl: severe (64): input conversion error, unit -5, file Internal Formatted Read
Image PC Routine Line Source
ypp 0000000001175E43 Unknown Unknown Unknown
ypp 000000000119953F Unknown Unknown Unknown
ypp 00000000011972F5 Unknown Unknown Unknown
ypp 000000000049564E Unknown Unknown Unknown
ypp 000000000040DF03 Unknown Unknown Unknown
ypp 0000000000407741 Unknown Unknown Unknown
libc-2.17.so 00002AEB94D173D5 __libc_start_main Unknown Unknown
ypp 0000000000406569 Unknown Unknown Unknown

Best regards,
Liu

Dear Liu,

But I don't know when the cutoff coulomb potential needs to be added, and how it fits into the example of the hBN band structure.

Yes, you need to consider a truncated Coulomb interaction otherwise the convergence with respect to the vacuum is very slow. In the FAQ you can find a thread on how to use it. It is activated adding the (-r) option in the command line and it is calculated once for all and then used for all the tasks (screened potential, GW; BSE).

ypp -J 2D_WR_WC -e s 1

Do you have the 2D_WR_WC directory? Can you post the report of your BSE calculation?

Best,
Daniele

Dear Daniele,
Thank you for your reply.

Yes, i have the 2D_WR_WC directory. The report of the BSE calculation is pasted below.

Best,
Liu

Dear Dr. LIU Hongling,
it is an I/O problem, but I cannot see anything weird in your report.

What happen if you copy your ndb.BS* files now in 2D_WR_WC into the SAVE directory and simply run:
ypp -e s 1

Do your compiled ypp works for other tasks, e.g. what happens if you launch:
ypp -e a -J 2D_WR_WC
is an input file created?

If you need to look at your exciton energies anyway it is possible to access them directly from the
ndb.BS_diago_Q1 database by using the ncdump command and redirectong the formatted text into a file.

Best,
Daniele

Dear Daniele,
I'm sorry to reply you so late.
I typed the command by mistake, and now the problem is solved.
Thank you very much.

Best,
LIU