Neglecting acoustic sum rule

[NFH]

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!

[hpaudya1]

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

[NFH]

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