Band structure of bulk graphene: Difference between revisions

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(Created page with "<pre> import numpy as np 2 from math import sqrt 3 from sys import argv 4 from ase import Atoms 5 from ase.lattice.surface import hcp0001 6 from gpaw import GPA...")
 
 
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==Graphene using grid==
*graphene_grid.py:
<pre>
<pre>
import numpy as np
from gpaw import GPAW, FermiDirac
2  from math import sqrt
from ase import Atoms
3  from sys import argv
from ase.io import read, write
4  from ase import Atoms  
from gpaw import GPAW, PoissonSolver, Mixer
5  from ase.lattice.surface import hcp0001
from ase.structure import bulk
6  from gpaw import GPAW, restart, Mixer  
 
7 
 
8  a = 2.4437
# -------------------------------------------------------------
  9 # Set up graphene structure
# Bulk configuration
10  vacuum = 3
# -------------------------------------------------------------
11  atoms = Atoms(symbols='C2', positions=[(0.5*a,-sqrt(3)/6*a,vacuum),(0.5*a, +sqrt(3)/6*a, vacuum)],
 
12                cell=[(0.5*a,-0.5*3**0.5*a,0),
gnr = bulk('C', 'hcp', a=2.4612, c=6.709) # hexagonal close-packed (hpc)
13                      (0.5*a,+0.5*3**0.5*a,0),
gnr.positions=([[ 0. , 0., 0.], [ 1.23060,  0.7104873,  0. ]])
14                      (0.0,0.0,2*vacuum)])  
 
15  atoms.set_pbc((True,True,False))  
write('gr.traj', gnr)
16 
 
17  # Gamma-point calculation of graphene
# Make self-consistent calculation and save results
18  calc = GPAW(h=0.2, width=0.15, kpts=(1,1,1), xc='LDA')
calc = GPAW(h=0.18,
19  atoms.set_calculator(calc)  
            mode='fd', #finite difference(fd)
20  atoms.get_potential_energy()  
            xc='PBE',
21 
            kpts=(5,5,1),
22 
            occupations=FermiDirac(width=0.05, maxiter=2000),
23  kpts = [ (1/2.0, 1/3.0, 0) ]
            mixer=Mixer(beta=0.010, nmaxold=8, weight=100.0),
24 
            poissonsolver=PoissonSolver(eps=1e-12),
25  # Calculate one K-point with usesymm=True
            txt='band_sc.txt')
26  calc.set(kpts = kpts, usesymm=True, fixdensity=True)  
 
27  calc.get_potential_energy()  
gnr.set_calculator(calc)
28  eigs_True = calc.get_eigenvalues(kpt=0)  
gnr.get_potential_energy()
29 
calc.write('band_sc.gpw')
30  # Redo with the same K-point with usesymm=False
 
31  calc.set(kpts = kpts, usesymm=False, fixdensity=True)  
 
32  calc.get_potential_energy()  
 
33  eigs_False = calc.get_eigenvalues(kpt=0)  
from ase.dft.kpoints import ibz_points, get_bandpath
34 
points = ibz_points['hexagonal']
35  print eigs_True
G = points['Gamma']
36  print eigs_False
K = points['K']
37  assert abs(eigs_True[0]-eigs_False[0])<1e-4
M = points['M']
kpts, x, X = get_bandpath([K, G, M, K], gnr.cell, 60)
 
calc = GPAW('band_sc.gpw',
            mode='fd',
            kpts=kpts,
            txt='band_harris.txt',
            fixdensity=True,
            parallel={'domain': 1},
            eigensolver='cg', # 'cg' is allowed for grid method only
            usesymm=None,
            convergence={'bands': 'all'})
 
if calc.input_parameters['mode'] == 'lcao':
    calc.scf.reset()
 
 
calc.get_potential_energy()
ef = calc.get_fermi_level()
calc.write('band_harris.gpw')
 
# Extract eigenenergies into a file for plotting with some external package
 
import numpy as np
 
calc = GPAW('band_harris', txt=None)
eps_skn = np.array([[calc.get_eigenvalues(k,s)
                    for k in range(40)]
                    for s in range(1)]) - ef
 
f = open('bands.dat', 'w')
for n in range(8):
    for k in range(40):
        print >>f, k, eps_skn[0, k, n]
    print >>f
</pre>
 
==Graphene using LCAO==
 
*graphene_lcao.py:
 
<pre>
from gpaw import GPAW, FermiDirac
from ase import Atoms
from ase.io import read, write
from gpaw import GPAW, PoissonSolver, Mixer
from ase.structure import bulk
 
# -------------------------------------------------------------
# Bulk configuration
# -------------------------------------------------------------
 
gnr = bulk('C', 'hcp', a=2.4612, c=6.709)
 
gnr.positions=([[ 0. ,  0., 0.], [ 1.23060,  0.7104873, 0. ]])
 
write('gnr.traj', gnr)
 
# Make self-consistent calculation and save results
calc = GPAW(h=0.18,
            mode='lcao',
            xc='PBE',
            basis='szp(dzp)',
            kpts=(5,5,1),
            occupations=FermiDirac(width=0.05, maxiter=2000),
            mixer=Mixer(beta=0.010, nmaxold=8, weight=100.0),
            poissonsolver=PoissonSolver(eps=1e-12),
            txt='band_sc.txt')
 
gnr.set_calculator(calc)
gnr.get_potential_energy()
calc.write('band_sc.gpw')
 
from ase.dft.kpoints import ibz_points, get_bandpath
points = ibz_points['hexagonal']
G = points['Gamma']
K = points['K']
M = points['M']
kpts, x, X = get_bandpath([K, G, M, K], gnr.cell, 40)
 
calc = GPAW('band_sc.gpw',
            mode='lcao',
            xc='PBE',
            basis='szp(dzp)',
            kpts=kpts,
            txt='band_harris.txt',
            fixdensity=True,
            parallel={'domain': 1},
            usesymm=None,
            convergence={'bands': 'all'})
 
if calc.input_parameters['mode'] == 'lcao':
    calc.scf.reset()
 
calc.get_potential_energy()
ef = calc.get_fermi_level()
calc.write('band_harris.gpw')
 
# Extract eigenenergies into a file for plotting with some external package
 
import numpy as np
 
calc = GPAW('band_harris', txt=None)
eps_skn = np.array([[calc.get_eigenvalues(k,s)
                    for k in range(40)]
                    for s in range(1)]) - ef
 
f = open('bands.dat', 'w')
for n in range(8):
    for k in range(40):
        print >>f, k, eps_skn[0, k, n]
    print >>f
</pre>
</pre>

Latest revision as of 14:41, 17 November 2014

Graphene using grid

  • graphene_grid.py:
from gpaw import GPAW, FermiDirac
from ase import Atoms
from ase.io import read, write
from gpaw import GPAW, PoissonSolver, Mixer
from ase.structure import bulk 


# -------------------------------------------------------------
# Bulk configuration
# -------------------------------------------------------------

gnr = bulk('C', 'hcp', a=2.4612, c=6.709) # hexagonal close-packed (hpc)
gnr.positions=([[ 0. ,  0.,  0.], [ 1.23060,  0.7104873,  0. ]])

write('gr.traj', gnr)

# Make self-consistent calculation and save results
calc = GPAW(h=0.18,
            mode='fd', #finite difference(fd)
            xc='PBE',
            kpts=(5,5,1),
            occupations=FermiDirac(width=0.05, maxiter=2000),
            mixer=Mixer(beta=0.010, nmaxold=8, weight=100.0),
            poissonsolver=PoissonSolver(eps=1e-12),
            txt='band_sc.txt')

gnr.set_calculator(calc)
gnr.get_potential_energy()
calc.write('band_sc.gpw')



from ase.dft.kpoints import ibz_points, get_bandpath
points = ibz_points['hexagonal']
G = points['Gamma']
K = points['K']
M = points['M']
kpts, x, X = get_bandpath([K, G, M, K], gnr.cell, 60)

calc = GPAW('band_sc.gpw',
            mode='fd',
            kpts=kpts,
            txt='band_harris.txt',
            fixdensity=True,
            parallel={'domain': 1},
            eigensolver='cg', # 'cg' is allowed for grid method only
            usesymm=None,
            convergence={'bands': 'all'})

if calc.input_parameters['mode'] == 'lcao':
    calc.scf.reset()


calc.get_potential_energy()
ef = calc.get_fermi_level()
calc.write('band_harris.gpw')

# Extract eigenenergies into a file for plotting with some external package

import numpy as np

calc = GPAW('band_harris', txt=None)
eps_skn = np.array([[calc.get_eigenvalues(k,s)
                     for k in range(40)]
                    for s in range(1)]) - ef

f = open('bands.dat', 'w')
for n in range(8):
    for k in range(40):
        print >>f, k, eps_skn[0, k, n]
    print >>f

Graphene using LCAO

  • graphene_lcao.py:
from gpaw import GPAW, FermiDirac
from ase import Atoms
from ase.io import read, write
from gpaw import GPAW, PoissonSolver, Mixer
from ase.structure import bulk 

# -------------------------------------------------------------
# Bulk configuration
# -------------------------------------------------------------

gnr = bulk('C', 'hcp', a=2.4612, c=6.709)

gnr.positions=([[ 0. ,  0.,  0.], [ 1.23060,  0.7104873,  0. ]])

write('gnr.traj', gnr)

# Make self-consistent calculation and save results
calc = GPAW(h=0.18,
            mode='lcao',
            xc='PBE',
            basis='szp(dzp)',
            kpts=(5,5,1),
            occupations=FermiDirac(width=0.05, maxiter=2000),
            mixer=Mixer(beta=0.010, nmaxold=8, weight=100.0),
            poissonsolver=PoissonSolver(eps=1e-12),
            txt='band_sc.txt')

gnr.set_calculator(calc)
gnr.get_potential_energy()
calc.write('band_sc.gpw')

from ase.dft.kpoints import ibz_points, get_bandpath
points = ibz_points['hexagonal']
G = points['Gamma']
K = points['K']
M = points['M']
kpts, x, X = get_bandpath([K, G, M, K], gnr.cell, 40)

calc = GPAW('band_sc.gpw',
            mode='lcao',
            xc='PBE',
            basis='szp(dzp)',
            kpts=kpts,
            txt='band_harris.txt',
            fixdensity=True,
            parallel={'domain': 1},
            usesymm=None,
            convergence={'bands': 'all'})

if calc.input_parameters['mode'] == 'lcao':
    calc.scf.reset()

calc.get_potential_energy()
ef = calc.get_fermi_level()
calc.write('band_harris.gpw')

# Extract eigenenergies into a file for plotting with some external package

import numpy as np

calc = GPAW('band_harris', txt=None)
eps_skn = np.array([[calc.get_eigenvalues(k,s)
                     for k in range(40)]
                    for s in range(1)]) - ef

f = open('bands.dat', 'w')
for n in range(8):
    for k in range(40):
        print >>f, k, eps_skn[0, k, n]
    print >>f
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