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["BRUNEVAL Fabien 201177" <fabien.bruneval@cea.fr>]

Dear Tao,

The spacing between k-points needs to be regular in the GW implementation.
I would advise you to keep a Monkhorst-Pack grid and then try to interpolate 
the GW correction for the particular k-point you need.
As the GW correction is usually weakly k-dependent, this method should be 
accurate enough.

Regards,

Fabien





-------- Message d'origine--------
De: gaotaoscu@hotmail.com [mailto:gaotaoscu@hotmail.com]
Date: dim. 5/31/2009 12:25
À: forum@abinit.org
Objet : [abinit-forum] GW correction works for irregular k-point?
 
Dear All,
 
In my research, I need computing the indirect energy gap for Silicon. After 
the
calculation of GW correction of GAMMA, the K-point (0.0, 0.416666667,
0.416666667) in BZ of Si is needed. And I tried to use "standard" procedure by
using ngkpt and nshiftk and shiftkin the second DATASET. But I kept seeing
following errors, seems that the "standard" method only works for those 
regular
grid points, not for an irregular k-point. The errors are as follow,
 
" cchi0 : ERROR -
  kp=k-q-G0 not found
 ik =    1 k =     0.000000    0.166667    0.166667
 k-q =           0.000000    0.500000    0.500000
 leave_new : decision taken to exit ..."
 
Could you please to help to find what's wrong with my input file? 
 
Thanks very much in advance.
 
Best,
 
Tao
 
My input file are as follow,
 
"ndtset      4
kptopt   1            # Option for the automatic generation of k points
ngkpt    4 4 4        # Density of k points
# Dataset1: usual self-consistent ground-state calculation
# Definition of the k-point grid
nkpt1    10
prtden1  1         # Print out density

# Dataset2: calculation of kss file
# Definition of k-points
nkpt2    39             # A set of 19 k-points containing Gamma
nshiftk2  4
shiftk2  0.0 2/3  2/3 # This grid contains the Gamma point
         0.5 0.5 0.5
         0.5 0.0 0.5
         0.5 0.5 0.0
istwfk2  39*1                    # Option needed for Gamma
iscf2    -2             # Non self-consistent calculation
getden2  -1             # Read previous density file
nband2   9
nbandkss2 100        # Number of bands to store in KSS file
# Dataset3: Calculation of the screening (epsilon^-1 matrix)
optdriver3  3        # Screening calculation
getkss3     -1       # Obtain KSS file from previous dataset
nband3      25       # Bands to be used in the screening calculation
ecutwfn3    3.6      # Planewaves to be used to represent the wavefunctions
ecuteps3    6.0      # Dimension of the screening matrix
ppmfrq3    16.7 eV  # Imaginary frequency where to calculate the screening
# Dataset4: Calculation of the Self-Energy matrix elements (GW corrections)
optdriver4  4        # Self-Energy calculation
getkss4     -2       # Obtain KSS file from dataset 1
getscr4     -1       # Obtain SCR file from previous dataset
nband4      100      # Bands to be used in the Self-Energy calculation
ecutwfn4    5.0      # Planewaves to be used to represent the wavefunctions
ecutsigx4    6.0      # Dimension of the G sum in Sigma_x
                     # (the dimension in Sigma_c is controlled by npweps)
nkptgw4      1                # number of k-point where to calculate the GW
correction
kptgw4                       # k-points
      0.000    5/12    5/12
bdgw4       4  5             # calculate GW corrections for bands from 4 to 5

# Definition of the unit cell: fcc
acell  3*10.217        # This is equivalent to   10.217 10.217 10.217
rprim  0.0  0.5  0.5   # FCC primitive vectors (to be scaled by acell)
       0.5  0.0  0.5   
       0.5  0.5  0.0
# Definition of the atom types
ntypat  1         # There is only one type of atom
znucl 14          # 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, the only type is Silicon.
                         
# Definition of the atoms
natom 2           # There are two atoms
typat  1 1        # They both are of type 1, that is, Silicon.
xred              # Reduced coordinate of atoms
      0.0  0.0  0.0
      0.25 0.25 0.25
# Definition of the planewave basis set (at convergence 16 Rydberg 8 Hartree)
ecut 8.0          # Maximal kinetic energy cut-off, in Hartree
# Use only symmorphic operations
symmorphi 0
# Definition of the SCF procedure
nstep   10        # Maximal number of SCF cycles
diemac  12.0      # 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.
                  # Here, we follow the prescription for bulk silicon.
tolwfr  1.0d-10   
# This line added when defaults were changed (v5.3) to keep the previous, old
behaviour
  iscf 5 "
 
And the output file shows that the irregular k-point "(0.0, 0.416666667,
0.416666667)" has been contained in K-point grid of KSS file. The k-points in
th eoutput file are as follow,
 
   " kpt2   0.00000000E+00  1.66666667E-01  1.66666667E-01
              1.25000000E-01  1.25000000E-01  1.25000000E-01
              1.25000000E-01  0.00000000E+00  1.25000000E-01
              2.50000000E-01  1.66666667E-01  1.66666667E-01
              3.75000000E-01  1.25000000E-01  1.25000000E-01
              3.75000000E-01  0.00000000E+00  1.25000000E-01
              5.00000000E-01  1.66666667E-01  1.66666667E-01
             -3.75000000E-01  1.25000000E-01  1.25000000E-01
             -3.75000000E-01  0.00000000E+00  1.25000000E-01
             -2.50000000E-01  1.66666667E-01  1.66666667E-01
             -1.25000000E-01  1.25000000E-01  1.25000000E-01
             -1.25000000E-01  0.00000000E+00  1.25000000E-01
              2.50000000E-01  4.16666667E-01  1.66666667E-01
              3.75000000E-01  3.75000000E-01  1.25000000E-01
              3.75000000E-01  2.50000000E-01  1.25000000E-01
              3.75000000E-01  3.75000000E-01  0.00000000E+00
              5.00000000E-01  4.16666667E-01  1.66666667E-01
             -3.75000000E-01  3.75000000E-01  1.25000000E-01
             -3.75000000E-01  2.50000000E-01  1.25000000E-01
             -3.75000000E-01  3.75000000E-01  0.00000000E+00
             -2.50000000E-01  4.16666667E-01  1.66666667E-01
             -1.25000000E-01  3.75000000E-01  1.25000000E-01
              2.50000000E-01 -3.33333333E-01  1.66666667E-01
              3.75000000E-01  5.00000000E-01  1.25000000E-01
              5.00000000E-01 -3.33333333E-01  1.66666667E-01
             -3.75000000E-01 -3.75000000E-01  1.25000000E-01
             -3.75000000E-01  5.00000000E-01  1.25000000E-01
              2.50000000E-01 -8.33333333E-02  1.66666667E-01
              3.75000000E-01 -2.50000000E-01  1.25000000E-01
              0.00000000E+00  4.16666667E-01  4.16666667E-01
              3.75000000E-01  3.75000000E-01  3.75000000E-01
              5.00000000E-01  4.16666667E-01  4.16666667E-01
             -3.75000000E-01  3.75000000E-01  3.75000000E-01
             -2.50000000E-01  4.16666667E-01  4.16666667E-01
             -2.50000000E-01 -3.33333333E-01  4.16666667E-01
              5.00000000E-01 -8.33333333E-02  4.16666667E-01
              0.00000000E+00 -3.33333333E-01 -3.33333333E-01
             -2.50000000E-01 -3.33333333E-01 -3.33333333E-01
              0.00000000E+00 -8.33333333E-02 -8.33333333E-02 "

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