Dear Dr. Lorenzo Paulatto 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.
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. 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. I hope this is enough description to get a meaningful help. Any advice will be appreciated. Thank you. Best Regards, >* Hi,*>** Dear dfsgdv dfsdf, >* I will explain my problmes with a simpe example.*>**>* Why don't you explain >posting some useful details of the actual*calculation you have done? Assume I am doing the phonon dispersion [ ...] >* So basically my problem is that I have generated two phonon dispersion*>* >relation: Gamma to Z and Gamma to X, but the optical mode frequencies at*>* >Gamma in the two plots are different.*>** 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: <http://cmt.dur.ac.uk/sjc/thesis_prt/node62.html>) 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 & Universit? Paris 6 phone: +33 (0)1 44275 084 / skype: paulatz www: http://www-int.impmc.upmc.fr/~paulatto/ mail: 23-24/4?16 Bo?te courrier 115, 4 place Jussieu 75252 Paris C?dex 05 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121010/276e22fc/attachment.html -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121011/29502655/attachment.html
