EPW Forum

Dear all,

I'm doing reference calculation on the phonon self energy of a material with (physical meaningful) imaginary phonon modes.

From the documentation of EPW it says that the acoustic sum rule can be either: ‘simple’, ‘crystal’, ‘one-dim’ or ‘zero-dim’
However an asr_typ = "simple" wouldn't be meaningful when dealing with imaginary modes (especially at Gamma).
In a phonon calculation I would chose asr = ''no" to avoid unphysical shifts. Is this possible within EPW? Even if some coding would be necessary?
At the end I am only interested in linewiths of real modes, but asr_typ = ''simple' would lead to unphysical shifts of the frequencies.

thank you in advance!

Hi NFH,

It would be appreciated if you could sign your name and affiliation in your future posts.

You can use asr_typ = 'no' in EPW with a small modification in the code as the following.

1) replace
CALL set_asr2(asr_typ, nqc1, nqc2, nqc3, ifc, zstar, nat, ibrav_, tau_)
by
IF (asr_typ /= 'no') CALL set_asr2(asr_typ, nqc1, nqc2, nqc3, ifc, zstar, nat, ibrav_, tau_)

in io_epw.f90 line 643 (qe-v7.2)

2) set the following input flags in your input file
lifc = .true. ! (this requires ifc.q2r file in your save directory, see point #3 below)
asr_typ = 'no'

3) copy 'prefix.fc' (obtained from q2r.x in the phonon calculation) to 'ifc.q2r' in your save directory.

I hope it helps.

Happy EPWing,
Hari

Dear Hari,

thanks a lot for the reply. Reading in the force constants directly and bypassing set_asr2 was something I had in mind, but wasn't to sure if I neglect something important by skipping set_asr2. It worked for me flawlessly.

thanks again,
Nicki
MLU/MPI Halle, Germany