ABINIT Discussion Forums

Hi
I am trying to calculate band gap of GaP semiconductor but I get the following error?
symkpt.F90:251:ERROR
Chksymbreak=1 . It has been observed that the k point grid is not symmetric :
for the symmetry number 3
with symrc1= -1 -1 -1 0 0 1 0 1 0
the symmetric of the k point number 196 with components 0.000000E+00 0.000000E+00 -1.250000E-01
does not belong to the k point grid.
Read the description of the input variable chksymbreak,

can anybody tell me what's wrong?
the following is my Inputs
# Calculation of the GW correction to the direct band gap in Gamma
# Dataset 1: ground state calculation
# Dataset 2: calculation of the kss file
# Dataset 3: calculation of the screening (epsilon^-1 matrix for W)
# Dataset 4: calculation of the Self-Energy matrix elements (GW corrections)

ndtset 4
nspden 2
nsppol 2
nspinor 1

kptopt 1 # Option for the automatic generation of k points
ngkpt 4 4 4 # Density of k points
gwcalctyp 20

# Dataset1: usual self-consistent ground-state calculation
# Definition of the k-point grid
nkpt1 10
nshiftk1 4
shiftk1 0.0 0.0 0.0 # This grid is the most economical
0.5 0.0 0.0
0.0 0.5 0.0
0.0 0.0 0.5
prtden1 1 # Print out density


# Dataset2: calculation of kss file
# Definition of k-points
nkpt2 19 # A set of 19 k-points containing Gamma
nshiftk2 4
shiftk2 0.0 0.0 0.0 # This grid contains the Gamma point
0.0 0.5 0.5
0.5 0.0 0.5
0.5 0.5 0.0
istwfk2 19*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 0 # Screening calculation
getkss3 -1 # Obtain KSS file from previous dataset
nband3 25 # Bands to be used in the screening calculation
ecutwfn3 7.0 # Planewaves to be used to represent the wavefunctions
ecuteps3 7.0 # 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 50 # Bands to be used in the Self-Energy calculation
ecutwfn4 11.0 # Planewaves to be used to represent the wavefunctions
ecutsigx4 11.0 # 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 0.000 0.000 # (Gamma)
bdgw4 4 5 # calculate GW corrections for bands from 4 to 5


# Definition of the unit cell: fcc
acell 3*9.99

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 2
znucl 31 15

# Definition of the atoms
natom 2 # There are two atoms
typat 1 2
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 30 # Maximal kinetic energy cut-off, in Hartree

# Use only symmorphic operations
symmorphi 0

# Definition of the SCF procedure
nstep 500 # 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.

tolwfr 1.0d-10

# This line added when defaults were changed (v5.3) to keep the previous, old behaviour
iscf 7

from the GW1 manual:

The k-point reduced coordinates are specified in kptgw. At present, they MUST belong to the k-mesh used to generate the KSS file. Hence if you wish the GW correction in a particular k-point, you should choose a grid containing it. Usually this is done by taking the k-point grid where the convergence is achieved and shifting it such as at least one k-point is placed on the wished position in the Brillouin zone.

regards,

Nikola