[Pw_forum] negative frequency

[Mike Mehl]

Dear Ghosh,

If I've read the paper correctly, the paper you are looking at is 
entirely computational, not experimental, so basically you are trying to 
decide if pseudopotentials used in that paper and in your calculation 
are going to give the same result.  You're not comparing with 
experiment, which, as has been pointed out by others, is at a high 
temperature.  You want to compare your calculations to Ho's.

So have you tried to duplicate the frozen phonon calculations described 
in the paper?  Or, possibly better, Figure 3?


On 05/21/2010 05:41 AM, partha sarathi ghosh wrote:
> 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 <http://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
>
>
>
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-- 
Michael J. Mehl
Head, Center for Computational Materials Science
Naval Research Laboratory Code 6390
Washington DC