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["Wu Rongqin" <g0203654@nus.edu.sg>]

Dear all,

I use abinit to calculate dielectric properties of cubic perovskite SrTiO3 which is only stable at high temperature.

 

A,The result showed negative values at gamma point.

Phonon at Gamma, with non-analyticity in the

  direction (cartesian coordinates)  0.00000  0.00000  1.00000

 Phonon energies in Hartree :

  -4.486115E-04 -4.486105E-04 -2.927791E-05 -2.869101E-05 -2.868774E-05

   2.908060E-04  2.908060E-04  2.908060E-04  5.257838E-04  8.833161E-04

   8.833162E-04  1.555478E-03  2.653876E-03  2.653876E-03  3.533046E-03

 Phonon frequencies in cm-1    :

- -9.845885E+01 -9.845862E+01 -6.425758E+00 -6.296948E+00 -6.296231E+00

-  6.382455E+01  6.382455E+01  6.382455E+01  1.153962E+02  1.938655E+02

-  1.938655E+02  3.413880E+02  5.824585E+02  5.824585E+02  7.754140E+02

I have check the k point and energy cutoff. Is this result normal? Can softening happen at gamma point?

2, the effective charges seemed also unreasonable

1    7   1    3   -1.8723143702    0.0000000000

   2    7   1    3    0.0000000000    0.0000000000

   3    7   1    3    0.0000000000    0.0000000000

 

   1    7   2    3    0.0000000000    0.0000000000

   2    7   2    3   -4.8593631119    0.0000000000

   3    7   2    3    0.0000000000    0.0000000000

 

   1    7   3    3    0.0000000001    0.0000000000

   2    7   3    3    0.0000000000    0.0000000000

   3    7   3    3   -1.8723135534    0.0000000000

 

   1    7   1    4   -1.8723135534    0.0000000000

   2    7   1    4    0.0000000000    0.0000000000

   3    7   1    4    0.0000000000    0.0000000000

 

   1    7   2    4    0.0000000001    0.0000000000

   2    7   2    4   -1.8723135534    0.0000000000

   3    7   2    4    0.0000000000    0.0000000000

 

   1    7   3    4   -0.0000000001    0.0000000000

   2    7   3    4    0.0000000000    0.0000000000

   3    7   3    4   -4.8593631119    0.0000000000

 

   1    7   1    5   -4.8593631119    0.0000000000

the -4.8593631119 is for oxygen atom. Which should be less than -2!

 

Any comment will be appreciated!

Rongqin Wu