This comment by Abdul Muhaymin provides the following thread from the Quantum ESPRESSO mailing list which I'm including below (for me, I couldn't even visit the thread online because my browser told me that there was a security risk, so I clicked "accept risk and continue" but since I'm providing the contents here, you don't need to do that):
Is it possible to use the scissor operator in a TDDFT calculation
using turbo_davidson or turbo_lanczos?
Yes in turbo_lanczos: the keyword is "scissor" in the lr_control
namelist. But I do not remember if it is in Ry or eV.
There was a follow-up question about whether the units are in Ry or eV:
Dear Iurii, Thanks! It is not described in the docs, but I figured out
that the variable scissor is used here:
DO ibnd = 1,nbnd ! CALL zaxpy(ngk(1), CMPLX(-(et(ibnd,1)-scissor),0.0d0,DP), & &
spsi1(:,ibnd), 1, sevc1_new(:,ibnd,1), 1) ! ENDDO
Can you tell from this bit whether it is in Ry or eV? It seems from
lr_readin.f90 that the units aren't converted.
Best wishes, Michal
The answer was given here:
Scissor must be specified in Ry units.