The ABINIT Users Mailing List ( CLOSED )

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

If your atoms are at special position I guess that there are forces on
them? Then your lattice shall not be stable, shall it? And I guess it
is somehow natural to find some negative phonon frequency?
Note that I'm not at all an expert so may be someone can give you some
more accurate comments. I can mistake or also simply misunderstand
what your saying. But your result seems fine from what I understand.

regards
PMA

On 6/8/06, javier.torres@unito.it <javier.torres@unito.it> wrote:
> Dear Abinit Users
>
> I performed a response function calculation in order to get the phonons at 
> gamma point of AgB2... For this I used the optimized gometry of my system, 
> performed with ionmov 2 and optcell 2 as you can see in the attached files, 
> the obtained lattice parameters correspond to a stress tensor with components 
> smaller than 10^-8, the atomic coordinates were not optimized because the 
> atoms are special positions...
>
> The result of the phonon calculation with this geometry is a set of freqs 
> with very negative values of about -46 cm^-1 ... How can I get the adequate 
> geometry of my system to get the true frequencies???
>
> Kind regards
>
> F. T.
>
> OPT...
> # Hexagonal Primitive (P6/mmm) AgB2 GS SHIFTK  0 0 0
> # Geometric block
> spgroup  191
> acell   5.4424112657  5.4424112657  6.6707332527  #Experimental Values Lal
> angdeg  90 90 120
> ntypat  2
> znucl   47 5
> natom   3
> typat   1 2 2
> xred
>         0.0 0.0 0.0
>         1/3 2/3 1/2
>         2/3 1/3 1/2
> #
> # OPTCELL
> #
> ionmov   2
> optcell  2    #try opcell 2 too!!!
> tolmxf   1.0d-5
> ntime    50
> dilatmx  1.2
> strfact  10
> #
> # Methods and Parameters
> #
> intxc    0         #better for fft changed  disable for RF calc
> occopt   7         #added for metalic occupation Gaussian smearing
> tsmear   0.01      #convergence
> brav     4         #added for hexagonal lattice
> ixc      1
> ecut     30.0
> ecutsm   0.5
> ngkpt    10 10 10       #16x16x16 exceeds the limit of memory allocation with 
> kopt=2
> frzfermi 1
> nshiftk  1
> shiftk   0.0 0.0 0.0
> #
> # SCF defined in each dataset
> #
> nstep     1000
> #
> # DS_1 gs and density calculation
> #
> iscf     3
> kptopt   1
> kptgen   1
> toldfe   1.0d-12   #important for freqcalc
> #irdwfk  1
>
>
>
> Phon...
>
> # Hexagonal Primitive (P6/mmm) AgB2 GS SHIFTK  0 0 0
> ndtset 2
> # Geometric block
> spgroup  191
> acell   5.6504357844  5.6504357843  7.5478571140
> angdeg  90 90 120
> ntypat  2
> znucl   47 5
> natom   3
> typat   1 2 2
> xred
>         0.0 0.0 0.0
>         1/3 2/3 1/2
>         2/3 1/3 1/2
> #
> # Methods and Parameters
> #
> intxc    0         #better for fft changed  disable for RF calc
> occopt   7         #added for metalic occupation Gaussian smearing
> tsmear   0.01      #convergence
> brav     4         #added for hexagonal lattice
> ixc      1
> ecut     43.0
> ecutsm   0.5
> ngkpt    10 10 10       #16x16x16 exceeds the limit of memory allocation with 
> kopt=2
> #frzfermi 1
> nshiftk  1
> shiftk   0.0 0.0 0.0
> #
> # SCF defined in each dataset
> #
> nstep     1000
> #
> # DS_1 gs and density calculation
> #
> iscf1     3
> kptopt1   1
> kptgen1   1
> tolwfr1   1.0d-20   #important for freqcalc
> #irdwfk1   1
> #
> # DS_2 whole phonon
> #
>   rfphon2   1            # Will consider phonon-type perturbation
>  rfatpol2   1 3          # Only the first atom is displaced
>    rfdir2   1 1 1        # Along the first reduced coordinate axis
>     nqpt2   1            # One wavevector is to be considered
>      qpt2   0 0 0        # This wavevector is q=0 (Gamma)
>   kptopt2   2            # Automatic generation of k points, taking
>                         # into account the time-reversal symmetry only
>   tolvrs2   1.0d-10       # SCF stopping criterion
>     iscf2   3            # Self-consistent calculation, using algorithm 3
>   getwfk2   -1            # Read the ground-state wavefunctions


--
Pierre-Matthieu Anglade