The ABINIT Users Mailing List ( CLOSED )

[Josef Zwanziger <jzwanzig@gmail.com>]

If there are N atoms in the unit cell, there are 3N phonon
frequencies. At gamma (0,0,0) 3 of these will be at frequency zero
(corresponding to rigid translation of the whole structure) and the
other 3N-3 at positive frequencies, provided that the cell is
mechanically stable under the model and environmental conditions
(temperature and pressure) of the simulation.


Josef W. Zwanziger
Professor of Chemistry
Canada Research Chair in NMR Studies of Materials
Director, Nuclear Magnetic Resonance Research Resource (NMR-3)
Dalhousie University
Halifax, NS B3H 4J3 Canada
tel: +1 (902) 494-1960
fax: +1 (902) 494-1867
web: http://jwz.chem.dal.ca
jzwanzig@gmail.com, jzwanzig@dal.ca



2009/8/11 yx_pxmu <yx_pxmu@163.com>:
> Dear all,
>
> In principle ,do I definitely get positive phonon frequency at
> q=(0,0,0) after I relax the cell shape and ion position completely ? I met a
> problem of getting imaginary frequency after the relaxation of both the cell
> shape and ion position .
> Thanks for hint.
>
> Yuanxun
>
>
>
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