Dear Zhang,<br>The ASR "cures" the dynamical matrix or the force constant matrix., or maybe both. The ASR can be applied by q2r.x (calculation of force constants) or matdyn.x (calculation and diagonalization of the dynamical matrices). I do not know , and I wuld like to know, if one should apply it twice or only in one of the steps. <br>
In any case, the 0 frequency at Gamma and the slopes are consistent. <br>However, the you must check that frequencies that are far from zero change little due to the ASR. Moreover, if you study the convergence vs cutoffs (this may be long and painful), check that the convergence trend of the frequencies is towards the values given with the ASR. <br>
<br>Note that negative frequencies may indicate instabilities in the structure, e.g., atomic positions not relaxed. This does not seems to be the case in the ouputs that you sent. Negative frequencies at points other than Gamma uncover the so called dynamical instability. The dynamical instability indicates that using a larger supercell you can find relaxations of the atomic positions (and maybe a phase transition) that are avoided by the symmetry imposed by the smaller supercell. I do not know if the ASR can mask the dynamical instabilities.<br>
<br>Hope this helps.<br><br>eduardo<br>
<p>Dear Eduardo and Stefano,</p>
<p>Thank you for clear and careful explaination of my phonon problem.
I am now doing some tests and getting more experiences, because I am a
freshman in phonon calculation. </p>
<p>It seems to me that ASR can "force" the acoustic phonon at Gamma
point to zero. A naive thought is that can we just ignore it? In this
case, are there any problem that the slope of the phonon around Gamma
is incorrect, because ASR cure the problem of k=0, but what about other
points near it? </p><br clear="all"><br>-- <br>Eduardo Menendez