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[<ilukacevic@fizika.unios.hr>]

Dear colleagues.

I am trying to reproduce the phonon calculations done by [1] and [2] in the
cubic ZrO2. However, I am unable to reproduce the phonon frequencies 
correctly:

1] I do not reproduce the soft optical mode at the X ponit of the BZ.
2] I do not reproduce the degeracy of the 2 acoustic modes at the X point.
3] All 3 acoustic modes are unstable in my calcs at the X point.

This is an insert from the one of my outputs for the phonons at the X point

 Phonon frequencies in cm-1    :
- -5.078229E+02 -4.244537E+02 -1.864653E+02  3.341160E+02  3.655486E+02
-  4.372096E+02  6.722486E+02  7.056660E+02  7.798493E+02


I am using Teters' LDA psps for Zr and O (from abinit web site) which include
12 and 6 valence electrons respectively. I have checked the convergence with
respect ot ecut and ngkpt until phonon freq. are converged under 1 cm^-1. I do
not obtain any serious warning in my calcs, except that the last occ is 2.00
(but I think that does not influence the result since cubic ZrO2 is an
isolator).

I would appreciate any hints and help concernig this problem. An example of my
input files is given bellow. I am using abinit 5.8.4 on a Linux Debian 
cluster.

Thank you all in advance.

Yours
Igor Lukacevic


Refs

[1] Phys. Rev. Lett. 81, 3297 (1998)
[2] Phys. Rev. Lett. 78, 4063 (1997)


Input file

#ZrO2 crystal; fcc
#phonons at X point

 ndtset     4
 acell      3*9.46

 #DATASET 1
  prtden?1  1
  kptopt?1  1
  tolvrs?1  1.0d-19
  nstep?1   80

 #DATASET 2
  iscf?2   -2
  nqpt?2    0
  getwfk?2 -1
  getden?2 -1
  tolwfr?2  1.0d-20
  nstep?2   400

 #DATASET 3
  getden?3 -2
  getwfk?3 -1
  iscf?3   -2
  nqpt?3    1
  qpt?3     0.50d0  0.50d0  0.0d0
  rfdir?3   1 1 1
  tolwfr?3  1.0d-20
  nstep?3   400

#DATASET 4
  getwfk?4 -2
  getwfq?4 -1
  nqpt?4    1
  qpt?4     0.50d0  0.50d0  0.0d0    #X point on the fcc BZ
  rfatpol?4 1  2
  rfdir?4   1 1 1
  rfphon?4  1
  tolvrs?4  1.0d-6
  nstep?4   25

#Common data****************

  ixc       3
  kptopt    3
  nshiftk   4
  shiftk    0.5  0.5  0.5
            0.5  0.0  0.0
            0.0  0.5  0.0
            0.0  0.0  0.5
  ngkpt     3*10
   ecut     40

#structure

  angdeg    90  90  90
  brvltt   -1
  occopt    1
  ntime     30
  nstep     40
  spgroup   225
  natom     3
  nband     12
  ntypat    2
  typat     1 2 2
  xred      0.00  0.00  0.00
            0.25  0.25  0.25
            0.25  0.25  0.75
  znucl     40 8 8

    iscf    7              # Use Pulay mixing sheme for SCF cycle
npulayit    10             # Number of Pulay iterations
  nnsclo    4              # Number of non-self consistent loops
   nline    8              # Number of line minimisations

  diemac    4

  timopt    2