The ABINIT Users Mailing List ( CLOSED )

[truefriends@163.com]

Hi all,

   Happy new year to you!
   
   Recently, I performed phonon dispersion calculations for bcc metal Ta, but 
I
obtained the strange dispersion curves that confused me much. That is, the 
curves from Gamma point to H point and from H to P point are both three 
branches, different with exp., two branches. 

   I have tested many input parameters such as ngkpt, nband, ecut, occopt, 
tsmear, ixc, iscf, shiftk, tolwfr, and the number of q mesh from 4*4*4 to 
8*8*8, but the number of the branches are always 3. The qpath and the main 
input file are listed below.If you have ever met the same problem, please 
give 
me a hand. Any information are appreciated very much. Thank you in advance!

Best regards,

Z. Liu

The Q-Path:
=========================================================================

  nph1l    41      ! number of phonons in list 1                             

  qph1l   0.000000000  0.000000000  0.000000000   1.0    !(gamma point)
          0.000000000  0.050000000  0.000000000   1.0
          0.000000000  0.100000000  0.000000000   1.0
          0.000000000  0.150000000  0.000000000   1.0
          0.000000000  0.200000000  0.000000000   1.0
          0.000000000  0.250000000  0.000000000   1.0
          0.000000000  0.300000000  0.000000000   1.0
          0.000000000  0.350000000  0.000000000   1.0
          0.000000000  0.400000000  0.000000000   1.0
          0.000000000  0.450000000  0.000000000   1.0
          0.000000000  0.500000000  0.000000000   1.0    !(H point)
          0.025000000  0.475000000  0.025000000   1.0
          0.050000000  0.450000000  0.050000000   1.0
          0.075000000  0.425000000  0.075000000   1.0
          0.100000000  0.400000000  0.100000000   1.0
          0.125000000  0.375000000  0.125000000   1.0
          0.150000000  0.350000000  0.150000000   1.0
          0.175000000  0.325000000  0.175000000   1.0
          0.200000000  0.300000000  0.200000000   1.0
          0.225000000  0.275000000  0.225000000   1.0
          0.250000000  0.250000000  0.250000000   1.0    !(P point)
          0.225000000  0.225000000  0.225000000   1.0
          0.200000000  0.200000000  0.200000000   1.0
          0.175000000  0.175000000  0.175000000   1.0
          0.150000000  0.150000000  0.150000000   1.0
          0.125000000  0.125000000  0.125000000   1.0
          0.100000000  0.100000000  0.100000000   1.0
          0.075000000  0.075000000  0.075000000   1.0
          0.050000000  0.050000000  0.050000000   1.0
          0.025000000  0.025000000  0.025000000   1.0
          0.000000000  0.000000000  0.000000000   1.0    !(gamma point)
          0.025000000  0.025000000  0.000000000   1.0
          0.050000000  0.050000000  0.000000000   1.0
          0.075000000  0.075000000  0.000000000   1.0
          0.100000000  0.100000000  0.000000000   1.0
          0.125000000  0.125000000  0.000000000   1.0
          0.150000000  0.150000000  0.000000000   1.0
          0.175000000  0.175000000  0.000000000   1.0
          0.200000000  0.200000000  0.000000000   1.0
          0.225000000  0.225000000  0.000000000   1.0
          0.250000000  0.250000000  0.000000000   1.0    !(N point)

  nph2l    1       ! number of directions in list 2

  qph2l   1.0  0.0  0.0    0.0
=========================================================================

The main input file:
=========================================================================
# Crystalline Ta : computation of the phonon spectrum

   ndtset   10
#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       2.50000000E-01  0.00000000E+00  0.00000000E+00
       qpt5       5.00000000E-01  0.00000000E+00  0.00000000E+00
       qpt6       2.50000000E-01  2.50000000E-01  0.00000000E+00
       qpt7       2.50000000E-01  2.50000000E-01  2.50000000E-01
       qpt8      -2.50000000E-01  2.50000000E-01  2.50000000E-01
       qpt9       5.00000000E-01  5.00000000E-01  2.50000000E-01
       qpt10      5.00000000E-01  5.00000000E-01  5.00000000E-01

#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 1        # 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

#################################  

  ecut 70
 

#  Options for the choice of calculation:
# ----------------------------------------
  ixc 11  occopt 6  tsmear 0.04
  
  nband 16
 
  
#  Definition of the unit cell:
# ------------------------------

  acell   3*6.24
  rprim  -0.5   0.5   0.5
          0.5  -0.5   0.5
          0.5   0.5  -0.5
  natom 1  ntypat 1
  typat 1*1  znucl 73.
  xred   0.  0.  0.
 

#  Definition of the k-point grid

  ngkpt   4 4 4
 


  nshiftk 2         # of the reciprocal space (that form a BCC lattice !),
                  # repeated four times, with different shifts :
  shiftk 
        0.25  0.25  0.25
       -0.25 -0.25 -0.25

#  Symmetries of the lattice:
# ----------------------------
  nsym 0
#
  iscf 5
=========================================================================