Hi Umesh, If you are interested in sorting overlapping phonon branches so that you can plot them, then you need to sort them at each q point based on the phonon eigenvector like Stefano noted. You can find this in the output from the matdyn calculation.
Keith Refson developed a script to sort phonon branches and plot them correctly based on eigenvectors for DFPT phonon calculations using CASTEP. Overrall, it does a very good job. I wrote a small script that converts the QE output to the CASTEP format. If you are interested, I can send you a copy of the codes. Best regards, Derek Derek Stewart Principal Research Scientist HGST, A Western Digital Company [email protected]<mailto:[email protected]> Office: (408) 717-5901 [HGST_aWDco_closing_sm_wLLD] 3403 Yerba Buena Rd San Jose, CA 95135 From: [email protected] [mailto:[email protected]] On Behalf Of Umesh Roy Sent: Saturday, August 1, 2015 4:22 AM To: [email protected] Subject: [Pw_forum] Separation between acoustic modes and optical modes Dear All, I have calculated modes of vibration of Iron in different directions for a fix phonon wave vector q (in a large number of directions). Since in Quantum espresso phonon modes are printed in increasing order for a given q vector. For a small group of q the acoustic and optical branches do not overlap so, we can easily separate out the acoustic branch from the optical branch. As we increase the magnitude of q the acoustic branch and the optical branch get mixed up. So , how to separate out the acoustic modes or is there any way of filtering the optical modes? Thank you in advance Umesh Chandra Roy Research Scholar, School of Physical Sciences Jawaharlal Nehru University, New Delhi-110067, India. Email:[email protected]<mailto:email%[email protected]> Mobile:+919868022722
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