[Pw_forum] a lot of negative phonons

[Muhammad Adnan]

Hello everyone
i am beginner of Q-E and was previously working with VASP.
i am calculating phonons for TiO2 anatase but i always get a lot of
negative frequencies. i have even used very dense KP grid and high cutoff
for wfc and c.density (60 and 700) but the problem persists.
if optimize the same structure with VASP and compute phonons then i do not
get any negative frequency.
what could be the possible reason for these negative phonons computed by
Q-E and not by vasp? and how can i improve my calculations? please someone
help me.
kind regards
Adnan
UFJF
Brazil
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