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[Anglade Pierre-Matthieu <anglade@gmail.com>]

Hello,

Frequently, unrelaxed cell parameters lead to negative phonon
frequencies at gamma. Seeing your values for acell, I wonder if you
have taken care to relax your cell structure using the same parameters
(ecut, kpt, tsmear, occopt ...)  before trying to get phonon
frequencies.

Regards

PMA


On Wed, Sep 9, 2009 at 8:46 AM, Sanjeev Kumar
Gupta<skgupta.physics@gmail.com> wrote:
> Dear ABINIT users,
> Greetings...
>
> I want to calculate phonon frequencies of GaP system (semiconductor), the
> input file, for that i got from abinit/tutorial.
> when i run this file (input file is given below), i got negative phonon
> frequencies at gamma point and no LO-TO separation.
>
> I have also given here, the output after running this input file. please
> suggest me, where i am wrong? I have seen all earlier posting related with
> this subject, but i can not resolve this problem.
>
> kind regards
> sanjeev
>
>
>
>
> # Crystalline GaP : computation of the response to homogeneous
>
> # electric field and atomic displacements, at q=0
>
>
>
>
>
>
>
>   ndtset  3
>
>
>
>
>
> #Ground state calculation
>
>   kptopt1   1             # Automatic generation of k points, taking
>
>                           # into account the symmetry
>
>   tolvrs1   1.0d-20     # SCF stopping criterion
>
>     iscf1   7             # Self-consistent calculation, using algorithm 7
>
>
>
>
>
> #Response Function calculation : d/dk
>
>   rfelfd2   2             # Activate the calculation of the d/dk
> perturbation
>
>    rfdir2   1 1 1         # Need to consider the perturbation in the all
> direction
>
>
>
>     nqpt2   1
>
>      qpt2   0.0 0.0 0.0   # This is a calculation at the Gamma point
>
>
>
>
>
>   getwfk2   -1            # Uses as input the output wf of the previous
> dataset
>
>
>
>
>
>   kptopt2   2             # Automatic generation of k points,
>
>                           # using only the time-reversal symmetry to
> decrease
>
>                           # the size of the k point set.
>
>
>
>
>
>     iscf2  -3             # The d/dk perturbation must be treated
>
>                               # in a non-self-consistent way
>
>   tolwfr2   1.0d-22       # Must use tolwfr for non-self-consistent
> calculations
>
>
>
> #Response Function calculation : electric field perturbation and phonons
>
>   rfphon3   1             # Activate the calculation of the atomic
> dispacement perturbations
>
>  rfatpol3   1 2          # All the atoms will be displaced
>
>   rfelfd3   3              # Activate the calculation of the electric field
> perturbation
>
>    rfdir3   1 1 1         # All directions are selected. However, symmetries
> will be used to decrease
>
>                                 # the number of perturbations
>
>     nqpt3   1
>
>      qpt3   0.0 0.0 0.0   # This is a calculation at the Gamma point
>
>
>
>
>
>   getwfk3   -2            # Uses as input wfs the output wfs of the dataset
> 1
>
>   getddk3   -1            # Uses as input ddk wfs the output of the dataset
> 2
>
>
>
>
>
>   kptopt3   2             # Automatic generation of k points,
>
>                           # using only the time-reversal symmetry to
> decrease
>
>                           # the size of the k point set.
>
>   tolvrs3   1.0d-9
>
>     iscf3   7             # Self-consistent calculation, using algorithm 7
>
>
>
>
>
>
>
>
>
> #######################################################################
>
> #Common input variables
>
>
>
>
>
> #Definition of the unit cell
>
> acell 3*10.45          # This is equivalent to   10.61 10.61 10.61
>
> rprim  0.0  0.5  0.5
>
>        0.5  0.0  0.5
>
>        0.5  0.5  0.0
>
>
>
>
>
> #Definition of the atom types
>
> ntypat 2               # There are two types of atom
>
> znucl 31 15
>
>
>
>
>
> #Definition of the atoms
>
> natom 2                # There are two atoms
>
> typat 1 2
>
> xred
>
>    0.0  0.0  0.0
>
>    0.25 0.25 0.25
>
>
>
>
>
> #Gives the number of band, explicitely
>
> nband  16
>
>
>
>
>
> #Exchange-correlation functional
>
> ixc 11
>
> #Definition of the planewave basis set
>
>  ecut    50.0           # Maximal kinetic energy cut-off, in Hartree
>
>
>
>
>
> #Definition of the k-point grid
>
> kptrlatt -4  4  4      # In cartesian coordinates, this grid is simple
> cubic, and
>
>           4 -4  4       # actually corresponds to the so-called 8x8x8
> Monkhorst-Pack grid.
>
>           4  4 -4
>
>           tsmear   0.04
>
>           occopt   4
>
>
>
>
>
>
>
> #Definition of the SCF procedure
>
> nstep 100               # Maximal number of SCF cycles
>
> diemac 10.0
>
>
>  
> ............................................................................................
>
> ouput
>
>
> Phonon wavevector (reduced coordinates) :  0.00000  0.00000  0.00000
>
>  Phonon energies in Hartree :
>
>   -1.028821E-04 -1.028819E-04 -1.028810E-04  1.468314E-03  1.468314E-03
>
>    1.468314E-03
>
>  Phonon frequencies in cm-1    :
>
> - -2.258001E+01 -2.257997E+01 -2.257978E+01  3.222577E+02  3.222577E+02
>
> -  3.222577E+02



-- 
Pierre-Matthieu Anglade