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[Sanjeev Kumar Gupta <skgupta.physics@gmail.com>]

Dear ABINIT users,

Greetings...

 

I want to calculate phonon frequencies of GaP system (semiconductor), the input file, for that i got from abinit/tutorial.

when i run this file (input file is given below), i got negative phonon frequencies at gamma point and no LO-TO separation.

 

I have also given here, the output after running this input file. please suggest me, where i am wrong? I have seen all earlier posting related with this subject, but i can not resolve this problem.

 

kind regards

sanjeev

 

 

 

# Crystalline GaP : computation of the response to homogeneous

# electric field and atomic displacements, at q=0

 

 

 

  ndtset  3

 

 

#Ground state calculation

  kptopt1   1             # Automatic generation of k points, taking

                          # into account the symmetry

  tolvrs1   1.0d-20     # SCF stopping criterion

    iscf1   7             # Self-consistent calculation, using algorithm 7

 

 

#Response Function calculation : d/dk

  rfelfd2   2             # Activate the calculation of the d/dk perturbation

   rfdir2   1 1 1         # Need to consider the perturbation in the all direction

                        

    nqpt2   1

     qpt2   0.0 0.0 0.0   # This is a calculation at the Gamma point

 

 

  getwfk2   -1            # Uses as input the output wf of the previous dataset

 

 

  kptopt2   2             # Automatic generation of k points,

                          # using only the time-reversal symmetry to decrease

                          # the size of the k point set.

 

 

    iscf2  -3             # The d/dk perturbation must be treated

                              # in a non-self-consistent way

  tolwfr2   1.0d-22       # Must use tolwfr for non-self-consistent calculations

                                   

#Response Function calculation : electric field perturbation and phonons

  rfphon3   1             # Activate the calculation of the atomic dispacement perturbations

 rfatpol3   1 2          # All the atoms will be displaced

  rfelfd3   3              # Activate the calculation of the electric field perturbation

   rfdir3   1 1 1         # All directions are selected. However, symmetries will be used to decrease

                                # the number of perturbations

    nqpt3   1

     qpt3   0.0 0.0 0.0   # This is a calculation at the Gamma point

 

 

  getwfk3   -2            # Uses as input wfs the output wfs of the dataset 1

  getddk3   -1            # Uses as input ddk wfs the output of the dataset 2

 

 

  kptopt3   2             # Automatic generation of k points,

                          # using only the time-reversal symmetry to decrease

                          # the size of the k point set.

  tolvrs3   1.0d-9

    iscf3   7             # Self-consistent calculation, using algorithm 7

 

 

 

 

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

#Common input variables

 

 

#Definition of the unit cell

acell 3*10.45          # This is equivalent to   10.61 10.61 10.61

rprim  0.0  0.5  0.5  

       0.5  0.0  0.5  

       0.5  0.5  0.0  

 

 

#Definition of the atom types

ntypat 2               # There are two types of atom

znucl 31 15           

 

 

#Definition of the atoms

natom 2                # There are two atoms

typat 1 2             

xred                  

   0.0  0.0  0.0       

   0.25 0.25 0.25     

 

 

#Gives the number of band, explicitely

nband  16             

 

 

#Exchange-correlation functional

ixc 11            

#Definition of the planewave basis set

 ecut    50.0           # Maximal kinetic energy cut-off, in Hartree

 

 

#Definition of the k-point grid

kptrlatt -4  4  4      # In cartesian coordinates, this grid is simple cubic, and

          4 -4  4       # actually corresponds to the so-called 8x8x8 Monkhorst-Pack grid.

          4  4 -4     

          tsmear   0.04   

          occopt   4   

 

  

 

#Definition of the SCF procedure

nstep 100               # Maximal number of SCF cycles

diemac 10.0           

 

 ............................................................................................

 

ouput

 

Phonon wavevector (reduced coordinates) :  0.00000  0.00000  0.00000

 Phonon energies in Hartree :

  -1.028821E-04 -1.028819E-04 -1.028810E-04  1.468314E-03  1.468314E-03

   1.468314E-03

 Phonon frequencies in cm-1    :

- -2.258001E+01 -2.257997E+01 -2.257978E+01  3.222577E+02  3.222577E+02

-  3.222577E+02