Dear Pw_users,<br><br>I am trying to do calculation phonon dispersion and EPC for 1D Aluminum chain. I got the results which are strange phonon branches appearing. In the case of 2 atom-cell, I got 4 phonon branches, two of them are Optical and Acoustical phonon branches and two others, which have zero and negative values, are unknown for me. In the case if I have 1 atom-cell, that strange branch also appears. Could any body explain for me what kind of frequencies here?
<br><br>I was surfing this forum and FAQ and I found many discussion about negative frequencies, but I still cannot find the answers for me.<br><br>Bac <br><br><br>This is my relaxed unitcell <br><br>For 1-atom cell<br><br>
input alat = 20.0000 (a.u.)<br><br>CELL_PARAMETERS (alat)<br> 0.999558675 0.000000000 0.000000000<br> 0.000000000 0.999558675 0.000000000<br> 0.000000000 0.000000000 0.224680571<br><br>ATOMIC_POSITIONS (angstrom)
<br>Al 0.000000000 0.000000000 0.000000000<br><br>For 2-atom cell<br><br>CELL_PARAMETERS (alat)<br> 1.000000000 0.000000000 0.000000000<br> 0.000000000 1.000000000 0.000000000<br> 0.000000000 0.000000000
0.453300000<br><br>ATOMIC_POSITIONS (angstrom)<br>Al 0.000000000 0.000000000 2.399000000<br>Al 0.000000000 0.000000000 0.000000000<br><br>And INPUT for ph.x <br><br> tr2_ph=1.0d-12,<br> prefix='al_20',
<br> fildvscf='Al2v',<br> amass(1)=26.98,<br> outdir='/root/tmp/',<br> fildyn='al2.dyn',<br> elph=.true.,<br> trans=.true.,<br> ldisp=.true.<br> nq1=1, nq2=1, nq3=10<br><br><pre>------------------------------
<br>Phung Viet Bac<br>Division of Mathematical and Physical Science,<br>Graduate School of Natural Science and Technology,<br>Kanazawa University,<br>Kakuma, Kanazawa 920-1192, JAPAN<br><br><br><br></pre><br><br>