Electron-Phonon Matrix Elements in Real Space g(R_e, R_p)

[Lai MingRui]

Dear Forum Moderators,

I am currently trying to compute the electron phonon matrix elements in real space for 2D MoS2. What I did was to change the subroutine bloch2wan.f90 to make it print out the matrix elements for each R_e, R_p, band index and mode.

In my scf and nscf calculation, I have used the assume_isolated = '2D' tag in QE. I have attached a link to the nscf, scf, epw and phonon input files here:

https://drive.google.com/open?id=1_Skvk ... VjBK3pkVPr

I am facing some difficulty with the computed matrix elements. To summarize, because this is a 2D system, I would expect that all of the R_p to be on the same plane. However, when I look at the data that was printed out, I noticed that half of the R_p vectors were pointing to a unit cell that is on a plane below the 2D system. I find this to be worrying because the system is suppose to be isolated.

I have checked the bandstructure computed using the MLWF and it perfectly fits the DFT computed bandstructure. I have also check the decay.epmat_wanep. It looks like the R_e's decays are normal, but the matrix elements does not decay well |R_p| increases.

I really appreciate any help that I could get on this, and also do let me know if more information is required!

Thank you all so much.

Best Regards,

Lai MingRui