ABINIT Discussion Forums

Hey,
I am trying to calculate the band structure of graphene and I used the attached input file. The bands look decent except the two bands highest in energy. If anyone knows why... please shed some light on this issue.
Thanks,
Rohan

# Crystalline graphene (graphite)
#
# Computation of the band structure.
# First, a SCF density computation, then a non-SCF band structure calculation.

ndtset 2

#Dataset 1 : usual self-consistent calculation
kptopt1 1 # Option for the automatic generation of k points,
# taking into account the symmetry
iscf1 3
nshiftk1 1
shiftk1 0 0 0.0 # These shifts will be the same for all grids

ngkpt1 5 5 1
nband1 8
prtden1 1 # Print the density, for use by dataset 2
toldfe1 1.0d-8

#Dataset 2 : the band structure
iscf2 -2
getden2 -1
kptopt2 -3
nband2 8
ndivk2 20 12 24 # 20, 12 and 24 divisions of the 3 segments, delimited
# by 4 points.
kptbounds2 0.0 0.0 0.0 # Gamma point
0.5 0.5 0.0 # M point
0.66667 0.33333 0.0 # K point
0.0 0.0 0.0 # Gamma point again

tolwfr2 1.0d-12
enunit2 1 # Will output the eigenenergies in eV


#Definition of the unit cell
acell 4.6415 4.6415 24.6415 # in Bohr radii
rprim 0.8660 -0.5 0 # Graphene (graphite) primitive column vectors scaled acell
0.8660 0.5 0
0 0 1

#Definition of the atom types
ntypat 1 # There is only one type of atom
znucl 6 # 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 Carbon

#Definition of the atoms: 2 atoms of type 1, Carbon
natom 2
typat 1 1
xangst # This keyword indicate that the location of the atoms in ANGSTROM
# will follow, one triplet of number for each atom
0.0 0.0 0.0 # Triplet giving the coordinate of atom 1.
0.71 1.22975 0.0 # Triplet giving the coordinate of atom 2.

#Definition of the planewave basis set
ecut 20.0 # Maximal kinetic energy cut-off, in Hartree

#Definition of the SCF procedure
nstep 25 # Maximal number of SCF cycles
diemac 1000000 # 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 a metal

Hi,

There is nothing wrong with your input file. In abinit, the 2 bands highest in energy are not as well converged as the others. If you want all of the bands in your band structure to look nice, calculate at least 2 more bands in your abinit calculations than you display in your final band structure.

Good luck,

Jonathan Laflamme Janssen

hai
I m now trying to plot the band structure and density of states of graphene. When I looked through the input file, I found the input variables 'acell' and 'rprim'.Can you help me to understand these input variables and how you have selected these for your input file.


Regards
Seba

Hi Dear
I'm new in abinit and use your input file for test.
i use pseudopotential:abinit-7.6.2/tests/Psps_for_tests/6c.pspnc. is it correct?
when run , see this error please help me:

chkinp: Checking input parameters for consistency.

chkinp: ERROR -
Chksymbreak=1 . A potentially symmetry-breaking value of tnons has been observed :
for the symmetry number 2
symrel is -1 0 0 0 -1 0 0 0 -1
tnons is -3.337787E-01 -3.324254E-01 0.000000E+00
Please, read the description of the input variable chksymbreak,
then, if you feel confident, you might switch it to zero, or consult with the forum.

chkinp: ERROR -
Chksymbreak=1 . A potentially symmetry-breaking value of tnons has been observed :
for the symmetry number 3
symrel is -1 0 0 0 -1 0 0 0 1
tnons is -3.337787E-01 -3.324254E-01 0.000000E+00
Please, read the description of the input variable chksymbreak,
then, if you feel confident, you might switch it to zero, or consult with the forum.

Seba Darshan wrote:hai
I m now trying to plot the band structure and density of states of graphene. When I looked through the input file, I found the input variables 'acell' and 'rprim'.Can you help me to understand these input variables and how you have selected these for your input file.


Regards
Seba

you can find your answer in this page : http://www.abinit.org/documentation/hel ... arbas.html
for initialize you need know graphene structure and try to optimize with K points,ecut and lattice parameters.
you can find more information in tutorial3 in abinit documents!

manzoor