This happens because<br>a) 0 frecuencies at Gamma occurs because the energy is is invariant with respect to arbitrary translations of the whole crystal (the same translation for all atoms). From this assumption the accoustic sum rule (ASR) is obtained theoretically. <br>
b) The plane wave DFT calculations do not have this invariance exactly, because of the plane wave cutoff. The energy is invariant not for arbitrary translations, but for translations in the FFT grid. <br>c) I guess that the absolute translation invariance is lost in the back and forth FFTs of the exchange-correlation potential, which is non linear, and probably in some part related with the ultrasoft pseudopotentials. Someone correct me if I am wrong, please.<br>
<br>You may increase the density cutoff (ecutrho) and see if the first three frequencies get closer to zero. First do it with one of the ESPRESSO examples, that run in minutes. I guess that I made that test some years ago. <br>
Using larger cutoffs increase a lot the calculation time. That is why you have the tricky option to impose the ASR in postprocessing (matdyn.x).<br><br>Practical way. If your "wrong" frecuencies are smaller than 50 cm^-1, this is normal. Apply the ASR in the input for matdyn. Check that the other frequencies do not change more than 1 or 2 cm^-1. Then, if this makes you happy, go to write your report<br>
<br>>I have another question about the output: What is the >difference
between the total magnetic moment and the >absolute magnetic moment.<br>This has been asked in the forum before. Please, google for this. If I remember well, the absolute magnetic moment is the integral of the absolute value of the magnetization. <br>
<br>Regards<br>Eduardo Menendez<br><br>On Sat, Jun 14, 2008 at 2:57 AM, <<a href="mailto:xwzhang@uestc.edu.cn" target="_blank">xwzhang@uestc.edu.cn</a>> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><p>Dear my pwscf friends,</p>
<p>Recently, I am trying to do phonon calculations in Heusler. As a
first step, I tried to reproduce the results of a paper by Zayak(PRB,
72, 054113, 2005). I choose Ni2MnGe as an example. To my surprise, the
acoustic branches at Gamma point gives a frequency of about 1 THz,
which should be zero. Other branches agree with the published data.</p>
<p>I wonder what might be the reason? I attached my scf, and phonon input files, and the phonon out put files. </p>
<p>I have another question about the output: What is the difference
between the total magnetic moment and the absolute magnetic moment.</p>
<p>Thank you and wish you a happy weekend!</p>
<p>Wenxu Zhang</p></blockquote><br>