<pre><font face="arial, helvetica, sans-serif">Dear Dr. Lorenzo Paulatto</font></pre><pre><font face="arial, helvetica, sans-serif">Hi, this is Kyeong. I was having hard time to figure out how to post questions on the PW_forum and tried different ways from different accounts. That's why my posting was from anonymous name. I also thought it might be easier to explain my problems with the simple example.</font></pre>
<pre><font face="arial, helvetica, sans-serif">Here's the real problem. I am generating phonon dispersion of bismuth telluride which has a rhombohedral structure with 5-point basis, and it generates 15 different frequency modes. As I explained in the previous message, the optical frequencys near gamma point are different depending on the propagation directions inside the FBZ. When I only calculated the frequencies at Gamma, it seemed okay, but it went weird as I added even one more q-vector to be calculated.</font></pre>
<pre><font face="arial, helvetica, sans-serif">I looked into my input files. I set the structure system as 'ibrav=5' (trigonal) because i found out that it's primitive cell is a simple rhombohedron. I set the K_POINTS as 'automatic 4 4 4 0 0 0' (This may be the one that I need to change to get symmetric structure), but I am not sure how to define the k points. To manage LO-TO splitting, I also set 'epsil=true'. That's pretty much what I have in my input files.</font></pre>
<pre><font face="arial, helvetica, sans-serif">I hope this is enough description to get a meaningful help. Any advice will be appreciated. Thank you.</font></pre><pre><font face="arial, helvetica, sans-serif">Best Regards,</font></pre>
<pre><br></pre><pre><br></pre><pre><br></pre><pre><br></pre><pre>><i> Hi,
</i>><i>
</i>
Dear dfsgdv dfsdf,
><i> I will explain my problmes with a simpe example.
</i>><i>
</i>><i> Why don't you explain posting some useful details of the actual
</i>calculation you have done?
Assume I am doing the phonon dispersion [ ...]
><i> So basically my problem is that I have generated two phonon dispersion
</i>><i> relation: Gamma to Z and Gamma to X, but the optical mode frequencies at
</i>><i> Gamma in the two plots are different.
</i>><i>
</i>
Either there is an error in your input, or the phonon code is smarter than
you. I.E. it is applying direction-dependent LO-TO splitting to the modes
at Gamma (one ref: <<a href="http://cmt.dur.ac.uk/sjc/thesis_prt/node62.html">http://cmt.dur.ac.uk/sjc/thesis_prt/node62.html</a>>)
If there is indeed a problem with your calculation, you should give us more
information in order to get meaningful help.
--
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www: <a href="http://www-int.impmc.upmc.fr/~paulatto/">http://www-int.impmc.upmc.fr/~paulatto/</a>
mail: 23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
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