Dear QE developers and users, I am using ph.x, q2r.x, and matdyn.x to calculate a phonon dispersion of a one-dimensional polymer (I am using vacuum in other two directions). I am using a phonon qgrid of 1*1*6 for the calculation of dispersion from ph.x. Later using q2r.x and matdyn.x, I am calculation phonon dispersion for 1*1*20 phonon qgrid.
My problem is that for the phonon qgrid of 1*1*6, I get non-negative frequencies at all of the irreducible phonon q points, but when I use matdyn.x to calculate phonon frequencies on 1*1*20, some of my acoustic modes frequencies are negative for non-gamma points! For instance, if my irreducible qpoints are 0.0, 0.1,0.3,0.5 (let say), then I get non-negative frequencies from ph.x for all four of these q points (which is right), but when I use matdyn.x to intepolate the frequencies, I get negative frequencies for lowest frequency acoustic phonons with q-points less than 0.1. I am using NORMCONS PP, electron k-grid = 1*1*12, with ecutwfc = 100 Ry, conv_thr=1.0d-12, tr2_ph = 1.0d-14, zasr/asr='one-dim' I am attaching my pw.in, ph.in, q2r.in and matdyn.in files with this mail. Thanks, Ankit Jain IIT Indore, India -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140418/6d89fdae/attachment.html -------------- next part -------------- A non-text attachment was scrubbed... Name: matdyn.in Type: application/octet-stream Size: 167 bytes Desc: not available Url : http://pwscf.org/pipermail/pw_forum/attachments/20140418/6d89fdae/attachment.obj -------------- next part -------------- A non-text attachment was scrubbed... Name: ph.in Type: application/octet-stream Size: 185 bytes Desc: not available Url : http://pwscf.org/pipermail/pw_forum/attachments/20140418/6d89fdae/attachment-0001.obj -------------- next part -------------- A non-text attachment was scrubbed... Name: pw.in Type: application/octet-stream Size: 875 bytes Desc: not available Url : http://pwscf.org/pipermail/pw_forum/attachments/20140418/6d89fdae/attachment-0002.obj -------------- next part -------------- A non-text attachment was scrubbed... Name: q2r.in Type: application/octet-stream Size: 94 bytes Desc: not available Url : http://pwscf.org/pipermail/pw_forum/attachments/20140418/6d89fdae/attachment-0003.obj