Regarding small negatve phonon frequency

[mirshowkat07]

Dear all
I want to perform electron-phonon calculation in EPW. I am getting a small negative phonon frequency in *.dyn1 file
which is also pasted below

After applying the acoustic sum rule, the phonon dispersion is positive in the whole Brillouin zone.
I want to know does the negative phonon frequency (in *.dyn1) affects the electron-phonon calculation.
That is, will the results be reliable?

freq ( 1) = -0.233565 [THz] = -7.790898 [cm-1]
freq ( 2) = 0.326763 [THz] = 10.899633 [cm-1]
freq ( 3) = 0.326763 [THz] = 10.899633 [cm-1]
freq ( 4) = 8.456742 [THz] = 282.086561 [cm-1]
freq ( 5) = 8.456742 [THz] = 282.086561 [cm-1]
freq ( 6) = 8.926573 [THz] = 297.758415 [cm-1]
freq ( 7) = 9.311704 [THz] = 310.605014 [cm-1]
freq ( 8) = 9.311704 [THz] = 310.605014 [cm-1]
freq ( 9) = 9.753003 [THz] = 325.325158 [cm-1]



with best regards
Showkat
HRI, India

[hlee]

Dear Showkat:

Negative phonon frequencies and additionally all phonon frequencies smaller than the value specified with eps_acustic (https://docs.epw-code.org/doc/Inputs.html#eps-acustic) are ignored in electron-phonon calculations.

Sincerely,

H. Lee