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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