Yambo Community Forum

Dear developers,

I am studying excited states in small-gap semiconductors with gaps smaller than 1 eV at PBE level. A realistic screening is important in order to reproduce experimentally measured exciton binding energies. My question is whether it is possible to use the scissor operator to shift the PBE energies to the corresponding GW energies in the computation of the response function (in the static screening computation)?

Dear Franz,

sure, you need to set the scissor and eventually the stretching in the XfnQP_E variable.
In order to make the variable appear in the input file, you need to increase the verbosity by adding (-V qp) in the command line to create the input file.

Best,

Daniele

Dear Daniele,

I did exactly what you suggested, but the results of the BSE that uses the 'scissored' screening does not differ from the BSE result obtained without applying the scissor. In both calculations I read the QP energies from the QP database. Could this lead to a conflict? I will attach the input file that I used for the scissored BSE calculation.

Best,
Franz

Dear Franz,

please check your input:
the correct syntax is: and not:

%
XfnQP_E
0.542180 | 1.000000 | 1.000000 |
%

Next, if screening was already calculated from a previous run and is stored in the SAVE directory, yambo reads it and eventually emits a warning if not all the variables in input are consistent with the ones read in the db. If this is what happened I should look at the report file.
A way to avoid it is to redirect databases e.g.

yambo -J screen_rpa
yambo -J screen_scissor

in this way the database are stored in the directory indicated with J option, they are not read by Yambo and recalculated.

Best,
Daniele

Dear Daniele,

thanks a lot for your help and for pointing out the error in my input file.

Best,
Franz