Crystalline iron
This example explains how to perform the density of states and band structure analyses by using crystalline iron (Fe) as an example.
SCF calculation
We begin with an SCF calculation. Input file looks like:
WF_OPT DAV
NTYP 1
NATM 1
BRAVIS_TYPE 1
NSPG 229
GMAX 5.00
GMAXP 15.00
KPOINT_MESH 08 08 08
MIX_ALPHA 0.50
BZINT TETRA
EDELTA 1.0D-10
NSPIN 2
NEG 16
XCTYPE ggapbe
CELL 5.40461887 5.40461887 5.40461887 90.00000000 90.00000000 90.00000000
&ATOMIC_SPECIES
Fe 55.845000 pot.Fe_pbe3
&END
&INITIAL_ZETA
0.2000
&END
&ATOMIC_COORDINATES CRYSTAL
0.0000 0.0000 0.0000 1 1 1
&END
We use the tetrahedron method for the Brillouin zone integration.
The total density of states printed to dos.data
can be visualized as:
NonSCF calculation
We can improve the quality of DOS by increasing the k-point mesh for the Brillouin zone integration without a new SCF calculation.
We use the keyword TASK NSCF
and perform a non-SCF calculation at a fixed charge density. Input file may look like:
TASK NSCF
WF_OPT DAV
NTYP 1
NATM 1
BRAVIS_TYPE 1
NSPG 229
GMAX 5.00
GMAXP 15.00
KPOINT_MESH 16 16 16
MIX_ALPHA 0.50
BZINT TETRA
EDELTA 1.0D-10
NSPIN 2
NEG 16
XCTYPE ggapbe
CELL 5.40461887 5.40461887 5.40461887 90.00000000 90.00000000 90.00000000
&ATOMIC_SPECIES
Fe 55.845000 pot.Fe_pbe3
&END
&INITIAL_ZETA
0.2000
&END
&ATOMIC_COORDINATES CRYSTAL
0.0000 0.0000 0.0000 1 1 1
&END
The total density of states may be visualized as:
Band structure calculation
As in the Ag case, set:
TASK BAND
after the SCF calculation is converged and run the calculation. The input file for the band structure may look like:
TASK BAND
WF_OPT DAV
NTYP 1
NATM 1
BRAVIS_TYPE 1
NSPG 229
GMAX 5.00
GMAXP 15.00
KPOINT_MESH 08 08 08
MIX_ALPHA 0.50
BZINT TETRA
EDELTA 1.0D-10
NSPIN 2
NEG 16
XCTYPE ggapbe
CELL 5.40461887 5.40461887 5.40461887 90.00000000 90.00000000 90.00000000
&ATOMIC_SPECIES
Fe 55.845000 pot.Fe_pbe3
&END
&INITIAL_ZETA
0.2000
&END
&ATOMIC_COORDINATES CRYSTAL
0.0000 0.0000 0.0000 1 1 1
&END
&KPOINTS_BAND
NKSEG 5
KMESH 30 30 20 30 30
KPOINTS
0.00 0.00 0.00
-0.50 0.50 0.50
0.00 0.00 0.50
0.25 0.25 0.25
0.00 0.00 0.00
0.00 0.00 0.50
&END
At the convergence, we obtain energy.data
in addition to the standard output files.
To convert the energy.data
file into a plottable one, use energy2band
program.
For the spin polarized system (NSPIN=2
), use
$ energy2band -s
Enter the number of bands, number of k-points (for the band structure calculation), and the energy origin (we use the Fermi level obtained in the SCF calculation or the valence band maximum), we obtain the band.data
file.
The band can be visualized by using gnuplot as: