The ABINIT Users Mailing List ( CLOSED )

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

If your structure is correct, or if you restrain yourself to lattice
constant optimisation, nothing except all the numbers you get.


On Tue, Nov 4, 2008 at 8:33 PM, Jedo <jedokim@umich.edu> wrote:
> Hi there,
>
> May be that is the reason.
> If I optimize the structure, what will change besides the lattice constant?
> Thanks for your help.
>
>
> Jedo
>
>
> Anglade Pierre-Matthieu wrote:
>>
>> Hi,
>> Have you optimised your cell before computing the phonons ? It looks
>> like you didn't. This could explain some negative phonons frequency.
>>
>> regards
>> PMA
>>
>> On Sat, Nov 1, 2008 at 2:21 AM,  <jedokim@umich.edu> wrote:
>>
>>>
>>> Hi all,
>>>
>>> I'm a new user of abinit and have some questions on my CaF2 phonon
>>> calculation. I end up with negative phonon frequency when I use response
>>> theory to calculate my phonons. Following is my input file and
>>> corresponding
>>> output file. Can someone help me? I tried everything from increasing the
>>> iteration numbers, increasing the cut off and lowering the conversion
>>> criteria. Please ignore the comment part.
>>> Thanks.
>>>
>>> Input
>>> # Crystalline AlAs : computation of the phonon spectrum
>>>
>>>  ndtset   5
>>> #Set 1 : ground state self-consistency
>>>
>>>  getwfk1   0            # Cancel default
>>>  kptopt1   1            # Automatic generation of k points, taking
>>>                        # into account the symmetry
>>>   nqpt1   0            # Cancel default
>>>  tolvrs1   1.0d-18      # SCF stopping criterion (modify default)
>>>  rfphon1   0            # Cancel default
>>>
>>> #Q vectors for all datasets
>>>
>>> #Complete set of symmetry-inequivalent qpt chosen to be commensurate
>>> # with kpt mesh so that only one set of GS wave functions is needed.
>>> #Generated automatically by running GS calculation with kptopt=1,
>>> # nshift=0, shiftk=0 0 0 (to include gamma) and taking output kpt set
>>> # file as qpt set. Set nstep=1 so only one iteration runs.
>>>
>>>    nqpt   1            # One qpt for each dataset (only 0 or 1 allowed)
>>>                        # This is the default for all datasets and must
>>>                        #  be explicitly turned off for dataset 1.
>>>
>>>    qpt2   0.00000000E+00  0.00000000E+00  0.00000000E+00
>>>    qpt3   0.00000000E+00  0.00000000E+00  0.00000000E+00
>>>    qpt4   -5.00000000E-01  0.00000000E+00  0.00000000E+00
>>>    qpt5   -5.00000000E-01  -5.00000000E-01  0.00000000E+00
>>>
>>>
>>>
>>> #Set 2 : Response function calculation of d/dk wave function
>>>
>>>   iscf2   -3         # Need this non-self-consistent option for d/dk
>>>  kptopt2   2          # Modify default to use time-reversal symmetry
>>>  rfphon2   0          # Cancel default
>>>  rfelfd2   2          # Calculate d/dk wave function only
>>>  tolvrs2   0.0        # Cancel default for d/dk
>>>  tolwfr2   1.0d-22    # Use wave function residual criterion instead
>>>
>>> #Set 3 : Response function calculation of Q=0 phonons and electric field
>>> pert.
>>>
>>>  getddk3   2          # d/dk wave functions from last dataset
>>>  kptopt3   2          # Modify default to use time-reversal symmetry
>>>  rfelfd3   3          # Electric-field perturbation response only
>>>
>>> #Sets 4-10 : Finite-wave-vector phonon calculations (defaults for all
>>> datasets)
>>>
>>>  getwfk   1          # Use GS wave functions from dataset1
>>>  kptopt   3          # Need full k-point set for finite-Q response
>>>  rfphon   1          # Do phonon response
>>>  rfatpol   1 3        # Treat displacements of all atoms
>>>   rfdir   1 1 1      # Do all directions (symmetry will be used)
>>>  tolvrs   1.0d-8     # This default is active for sets 3-10
>>>
>>> #######################################################################
>>> #Common input variables
>>>
>>> #Definition of the unit cell
>>>   acell   3*10.307         # This is equivalent to   10.61 10.61 10.61
>>>   rprim   0.0   0.5   0.5   # In lessons 1 and 2, these primitive vectors
>>>           0.5   0.0   0.5   # (to be scaled by acell) were 1 0 0  0 1 0
>>>  0
>>> 0 1
>>>           0.5   0.5   0.0   # that is, the default.
>>>
>>> #Definition of the atom types
>>>  ntypat   2         # There are two types of atom
>>>   znucl   20 9     # The keyword "znucl" refers to the atomic number of
>>> the
>>>                     # possible type(s) of atom. The pseudopotential(s)
>>>                     # mentioned in the "files" file must correspond
>>>                     # to the type(s) of atom. Here, type 1 is the
>>> Aluminum,
>>>                     # type 2 is the Arsenic.
>>>
>>> #Definition of the atoms
>>>   natom   3         # There are two atoms
>>>   typat   1 2 2       # The first is of type 1 (Ca), the second is of
>>> type
>>> 2 (F).
>>>
>>>    xred   0.0  0.0  0.0
>>>           0.25 0.25 0.25
>>>           0.75 0.75 0.75
>>>
>>> #Gives the number of band, explicitely (do not take the default)
>>>     nband  9
>>>
>>> #Exchange-correlation functional
>>>
>>> #     ixc   11             # LDA Teter Pade parametrization
>>>
>>> #Definition of the planewave basis set
>>>
>>>    ecut   100.0           # Maximal kinetic energy cut-off, in Hartree
>>>
>>> #Definition of the k-point grid
>>>   ngkpt   2  2  2
>>>  nshiftk   4              # Use one copy of grid only (default)
>>>  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
>>>
>>> #Definition of the SCF procedure
>>>    iscf   5          # Self-consistent calculation, using algorithm 5
>>>   nstep   200         # Maximal number of SCF cycles
>>>  diemac   7.0        # Although this is not mandatory, it is worth to
>>>                      # precondition the SCF cycle. The model dielectric
>>>                      # function used as the standard preconditioner
>>>                      # is described in the "dielng" input variable
>>> section.
>>>                      # The dielectric constant of AlAs is smaller that
>>> the
>>> one of Si (=12).
>>>
>>>
>>>
>>> OUT PUT
>>> Data set 5
>>>  Phonon wavevector (reduced coordinates) :  0.50000  0.50000  0.00000
>>>  Phonon energies in Hartree :
>>>  -2.309453E-03 -4.549870E-04  1.278573E-03  1.393728E-03  1.396572E-03
>>>  1.845115E-03  2.071170E-03  2.399689E-03  3.303399E-03
>>>  Phonon frequencies in cm-1    :
>>> - -5.068664E+02 -9.985810E+01  2.806144E+02  3.058879E+02  3.065122E+02
>>> -  4.049560E+02  4.545694E+02  5.266708E+02  7.250124E+02
>>>
>>>
>>> It seems that negative phonon start to appear from Data set 4.
>>>
>>>
>>>
>>
>>
>>
>>
>



-- 
Pierre-Matthieu Anglade