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["matthieu verstraete" <matthieu.jean.verstraete@gmail.com>]

On Mon, Nov 10, 2008 at 3:41 AM, Zhenhua Zeng <myid520@163.com> wrote:

Hello Everyone,

I'm callculating phonon of Pb(111) slab: 6 ML Pb with a vaccum about 12 \AA,
I found that
[1] the result printed out in the out file are not consistent with the results of anaddb.
[2] I.e. the results in out file seem meaningless.

For example the phonon at gamma  point:
out file(cm-1): 3.754035E+01  3.922919E+01  3.951580E+01  4.177673E+01 ....
anaddb  (cm-1): almost zero   almost zero   almost zero   about 1.0E+01 ....

anaddb imposes the acoustic sum rule, whereas abinit (in the single q phonon run) does not necessarily (not by default). The ASR error is quite large in your case (30cm-1) and shifts the other modes quite a lot too. It's probably correct, though, but you should check.

 

[2] why anaddb can give a 'reasonable' result, even though frequencies in the out file are so bad?

because the ASR error is systematic, and is subtracted out everywhere by the ASR correction. I should write up a note about this, 1 question out of 20 is on the same problem.

 

These parameters are ok for the phonon calculation of bulk  Pb.

in principle you should re-do convergence studies for the surface, but I suspect it should be ok. Check what the in-plane Fermi-surface is like!

Matthieu

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
Dpto. Fisica de Materiales, 
U. del Pais Vasco,            
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Mail : matthieu.jean.verstraete@gmail.com
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