The ABINIT Users Mailing List ( CLOSED )

["Aldo Humberto Romero" <aromero@qro.cinvestav.mx>]

Tom

you can do the calculation both ways but one of the strength
of Abinit is to have the implementation of response theory.
Everything is quite well described in the tutorials. In any
case, there are good places to read about it but there is
a PRB paper from X. Gonze, which explain the whole implementation
rather clear..

ifcflag 0 gives you zero frequencies.. that makes
sense, right.. no calculation of ifc then no frequencies..

One more note, Abinit has implementation for the Gamma point
in polar materials by using also response theory ... more
recently it also includes spin/orbit effects..

regards

/aldo.




> Dear all,
>    I wonder how abinit works to calculate phonon frequency. Dose it invoke
> so-called 'frozen phonon' approach (i.e. calculate the energy differences
> wrt
> given atomic displacements and then use second order polynomial in the
> phonon
> amplitudes to fit to these differences to reveal the coefficients of
> second
> order terms, namely the phonon frequencies)? Or, maybe, it just calculates
> the
> second derivatives of the energy to obtain the dynamic matrices and use
> force-contant model (just involving nearest neighbor interaction only) to
> calculate frequencies?
>     I notice that in 'anaddb', one can turn on 'ifcflag'(Interatomic Force
> Constants FLAG ) in the input file, does it mean the latter stated above
> is the
> way? I also note that if I set ifcflag to zero, i.e. calculate the
> frequencies
> directly from 'DDB' file, all the results are zero,  why?
>     Excuse me, perhaps too many questions in one mail.        :)
>
> sincerely,
> tom
> 07/25/2008
>


---------------------------------------------------
Prof. Aldo Humberto Romero
CINVESTAV-Unidad Queretaro
Libramiento Norponiente 2000
CP 76230, Queretaro, QRO, Mexico
tel: 442 211 9909
fax: 442 211 9938
email: aromero@qro.cinvestav.mx
       aldorome@gmail.com
www: qro.cinvestav.mx/~aromero