[Pw_forum] negative frequency

[partha sarathi ghosh]

Dear all,
                           Thank you xirainbow and Michael J. Mehlfor for
your reply & suggestion .
 I was trying to calculate longitudinal phonon dispersion of Zr along [111]
direction.
I wanted to validate my calculation with experimental results for bcc-Zr
(not hcp) given in the paper :Phy.Rev.B,vol-29,page 1575-1587(1984).
But I am getting negative frequencies near q=2/3(1 1 1) and the over all
appearance of the curve is different from the experimental one.  I optimized
the system w.r.t  ecutwf, ecutrho , k-point sampling , volume ,degauss,
conv_thr. I have also tried with different q-point sampling in ph.in file
(like 4 4 4, 8 8 8) with tr2_ph=1.0d-12.
My questions are :
1. Is DFTP suitable for studying particular phonon mode like in Zr ??
2. If yes then how to make my calculations efficient ??
3. If not then any suggestion of other methods ??
 Any one can please help me.
Thanks in advance.
P. S. Ghosh
B.A.R.C.
INDIA
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20100521/2ff212cf/attachment.html>