Yambo Community Forum

Dear yambo developers,
I'm using yambo to get a spectrum of GW. But I got a lot of o.ep_q_ip files. I know that the second column of data represents the imaginary part of the dielectric function. But I don't know which file's data is what I need.
I uploaded my input file and my output file. I hope I can get your help.

Dear WangFuyou,

in your input you set: so you are asking for the spectrum for several transferred momentum. If you are interested in "optical" spectrum, you need to look at the long wavelength limit q~0, while other q point spectrum are useful in the interpretation of electron-energy loss experiments where a finite momentum can be transferred.

In Yambo this limit is always the q index number 1, so you need to look at the o.eps_q1_ip file.

In general if you are interested in optics only you can set in the input: so avoiding calculating the spectrum for other momentum.

Best,
Daniele

Dear Daniele,
Thanks for your reply, now I understand the meaning of this parameter. But when I used the imaginary part of the dielectric function to plot the spectrum, I found that it was almost the same as the result obtained by DFT. I'm pretty sure there's something wrong with that. But I did set KfnQPdb = E <./FULL/ndb.QP.
I want to know what caused it. I guess it's a convergence problem. But I don't know how to tell that the convergence requirement is met, because I don't know how to get the band gap of GW.
I look forward to your guidance. Thank you very much.

Yours,
WangFuyou

Dear WangFuyou,

it seems the QP database has not been read. If you inspect the report file, at the end you find a mirror of the input variable used by Yambo in the run, and you can recognize that the KfnQPdb was not read.

Here there are two issues:
1) the database path should be inserted with quotes: "E < ./FULL/ndb.QP"
2) You are not in the BSE runlevel, and for a linear response calculation the right variable is XfnQPdb and not KfnQPdb

The general suggestion is to generate input by command line and not by hand:
in your case, the command line is:

> yambo -o c -V qp

The -V option adds verbosity in your input file, showing all the optional variables.

>yambo -h
gives you a help on how to generate input files.

Best,
Daniele

Dear Daniele,
Thank you for your answer. I ran the calculations again as you suggested. But it didn't work.
I found such a warning in the r_optics_dipoles_chi_01 file :
[WARNING]I/O problems in reading QP database ./FULL/ndb.QP
I wonder if the results of the QP were not successfully read.Looking forward for your help.

yours,
WangFuyou

Dear WangFuyou,

indeed, the QP file was not read. Do you have any error message in the log files l_* in the LOG directory?
This can help in spotting the problem.
Best,
Daniele