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[Mustafa Uludogan <uludoganmustafa@yahoo.com>]

Hi,
I try to calculate the frequency dependent dielectric
coefficients  for a typical cubic ABO3 ferroelectric
compound 
by anaddb variables 
 dieflag   1     ! 2=> electronic dielectric tensor
only
 nfreq     100
 frmin     0.0
 frmax     0.008
. I hav egotten the following output. 
If there are unstable modes present in the system, is
there a way to calculate these properties?

Yours 
Mustafa Uludogan




Relaxed ion dielectric tensor

phonon modes warning- :
unstable eigenvalue detected in force constant matrix
at Gamma point
the system under calculation is physically unstabale.
    -80.36253001      0.00013084      0.00008454
      0.00013084    -80.35369361     -0.00006049
      0.00008454     -0.00006049    -80.36250426

 diel9 : ERROR -
  The lowest mode appears to be a "true" negative
mode,
  and not an acoustic mode. This precludes the
computation
  of the frequency-dependent dielectric tensor.
  Action : likely there is no action to be taken,
although you,
  could try to raise your convergence parameters (ecut
and k-points).
 For your information, here are the four lowest
frequencies :
 -7.95442387E-04 -7.95418229E-04 -7.95418229E-04 
0.00000000E+00

 leave_new : decision taken to exit ...


Mustafa Uludogan
Chemical Engineering Department
Texas A&M University
College Station, TX 77843

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