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["Hua Bao" <hbao@purdue.edu>]

Title: problem of Si dielectric function calculation using optic

Dear All,

Abinit website comes back finally. ^_^

I am using "optic" to calculate the dielectric functions of different materials
I tried GaAs as in the material and also carbon nanotube. They work fine.

However, when I tried optic with bulk Si and Al2O3, I saw very minimal variations in the dielectric functions.
Basically they are just Im =0, and Re =1, the variation are in 10E-3 order.

We know that Si should have absorption peaks in visible range. Al2O3 should also have absorption above the bandgap (8 eV).

In principle, the optical properties can be determined using Fermi's golden rule as long as I have the band structure and wavefunctions. I don't know why I cannot get Si and Al2O3 work. Is it due to some physical reason or due to my mistakes in the input file.

Here is my input for Si. It is basically the same as GaAs. I tried finer k-grid (3*12) and larger cutoff (20 Ha), but nothing changed.

 ndtset 6

#First dataset : SC run with kpoints in the IBZ
   iscf1  3
  nband1  4
  nstep1 250
 kptopt1 1
 nbdbuf1 0
 prtden1 1   getden1 0   getwfk1 0    ! Usual file handling data

#Second dataset : NSC run with large number of bands, and points in the IBZ
    iscf2 -2
   nband2  20  ! Minimal number of bands for linear optics (imaginary part of the spectrum)
   nstep2 250
  kptopt2  1
  getwfk2  1   getden2 1   ! Usual file handling data

#Third dataset : NSC run with large number of bands, and points in the the full BZ
    iscf3 -2
   nband3  20  ! Minimal number of bands for linear optics (imaginary part of the spectrum)
   nstep3 250
  kptopt3  2  ! Time-reversal symmetry can be used in the present implementation for linear optics
  getwfk3  2   getden3 1   ! Usual file handling data

#Fourth dataset : ddk response function along axis 1
   iscf4 -3
  nband4  20   ! Minimal number of bands for linear optics (imaginary part of the spectrum)
  nstep4  1  nline4  0
 kptopt4  2   ! Time-reversal symmetry can be used in the present implementation for linear optics

   nqpt4  1  qpt4  0.0d0 0.0d0 0.0d0
  rfdir4  1 0 0
 rfelfd4  2
 getwfk4  3

#Fifth dataset : ddk response function along axis 2
   iscf5 -3
  nband5  20   ! Minimal number of bands for linear optics (imaginary part of the spectrum)
  nstep5  1  nline5  0
 kptopt5  2   ! Time-reversal symmetry can be used in the present implementation for linear optics

   nqpt5  1  qpt5  0.0d0 0.0d0 0.0d0
  rfdir5  0 1 0
 rfelfd5  2
 getwfk5  3

 Sixth dataset : ddk response function along axis 3
   iscf6 -3
  nband6  20   ! Minimal number of bands for linear optics (imaginary part of the spectrum)
  nstep6  1  nline6  0
 kptopt6  2   ! Time-reversal symmetry can be used in the present implementation for linear optics

   nqpt6  1  qpt6  0.0d0 0.0d0 0.0d0
  rfdir6  0 0 1
 rfelfd6  2
 getwfk6  3

#Data common to all datasets
 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*4       ! This is much too low : should be at least 24x24x24

 acell   3*10.217
# amu 69.72  74.9216
 diemac 10.0
 ecut 3.00             ! This is also too low
# iscf 3
# ixc 3
 natom  2  nbdbuf 2
 ntypat  1
 rprim   0 .5 .5  .5 0 .5  .5 .5 0
 xred 3*0.00d0 3*0.25d0
# tnons 72*0.0
 typat  1 1  tolwfr  1.e-22
 znucl  14