[Pw_forum] Negative freuqencies for extrapolating points

[Elio Physics]

Dear all,


I have calculated the frequencies for a structure. All frequencies were positive except for a few "extrapolated" points very close to the Gamma point which were negative in the range of -1.45 cm^-1. Due to this the dispersion curve near the Gamma point looked a bit funny (but looks pretty good elsewhere).  I tried the calculations with 2 different phonon grids. Any reason why this is happening? Do i have to lower  tr2_ph more (it is already 10^(-19)!)


Any help would be appreciated.


Elio

Fed Uni of Rondonia

Brazil

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