The ABINIT Users Mailing List ( CLOSED )

[<tomblister@hotmail.com>]

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