def test_inverse_transform():
# Define family on square lattice
s = spin_matrices(1 / 2)
# Time reversal
TR = PointGroupElement(
np.eye(2), True, False,
spin_rotation(2 * np.pi * np.array([0, 1 / 2, 0]), s))
# Mirror symmetry
Mx = PointGroupElement(
np.array([[-1, 0], [0, 1]]), False, False,
spin_rotation(2 * np.pi * np.array([1 / 2, 0, 0]), s))
# Fourfold
C4 = PointGroupElement(
np.array([[0, 1], [-1, 0]]), False, False,
spin_rotation(2 * np.pi * np.array([0, 0, 1 / 4]), s))
symmetries = [TR, Mx, C4]
# One site per unit cell
norbs = OrderedDict([('A', 2)])
# Hopping to a neighbouring atom one primitive lattice vector away
hopping_vectors = [('A', 'A', [1, 0])]
# Make family
family = bloch_family(hopping_vectors, symmetries, norbs)
fam = hamiltonian_from_family(family, tosympy=False)
# Atomic coordinates within the unit cell
atom_coords = [(0, 0)]
lat_vecs = [(1, 0), (0, 1)]
syst = model_to_builder(fam, norbs, lat_vecs, atom_coords)
# Convert it back
ham2 = builder_to_model(syst).tomodel(nsimplify=True)
# Check that it's the same as the original
assert fam == ham2
# Check that the Hamiltonians are identical at random points in the Brillouin zone
sysw = kwant.wraparound.wraparound(syst).finalized()
H1 = sysw.hamiltonian_submatrix
H2 = ham2.lambdify()
H3 = fam.lambdify()
coeffs = 0.5 + np.random.rand(3)
for _ in range(20):
kx, ky = 3 * np.pi * (np.random.rand(2) - 0.5)
params = dict(c0=coeffs[0], c1=coeffs[1], c2=coeffs[2], k_x=kx, k_y=ky)
assert allclose(H1(params=params), H2(**params))
assert allclose(H1(params=params), H3(**params))
def test_graphene_to_kwant():
norbs = OrderedDict([('A', 1), ('B', 1)
]) # A and B atom per unit cell, one orbital each
hopping_vectors = [('A', 'B', [1, 0])
] # Hopping between neighbouring A and B atoms
# Atomic coordinates within the unit cell
atom_coords = [(0, 0), (1, 0)]
# We set the interatom distance to 1, so the lattice vectors have length sqrt(3)
lat_vecs = [(3 / 2, np.sqrt(3) / 2), (3 / 2, -np.sqrt(3) / 2)]
# Time reversal
TR = PointGroupElement(sympy.eye(2), True, False, np.eye(2))
# Chiral symmetry
C = PointGroupElement(sympy.eye(2), False, True, np.array([[1, 0], [0,
-1]]))
# Atom A rotates into A, B into B.
sphi = 2 * sympy.pi / 3
RC3 = sympy.Matrix([[sympy.cos(sphi), -sympy.sin(sphi)],
[sympy.sin(sphi), sympy.cos(sphi)]])
C3 = PointGroupElement(RC3, False, False, np.eye(2))
# Generate graphene Hamiltonian in Kwant from qsymm
symmetries = [C, TR, C3]
# Generate using a family
family = bloch_family(hopping_vectors, symmetries, norbs)
syst_from_family = model_to_builder(family,
norbs,
lat_vecs,
atom_coords,
coeffs=None)
# Generate using a single Model object
g = sympy.Symbol('g', real=True)
ham = hamiltonian_from_family(family, coeffs=[g])
ham = Model(hamiltonian=ham, momenta=family[0].momenta)
syst_from_model = model_to_builder(ham, norbs, lat_vecs, atom_coords)
# Make the graphene Hamiltonian using kwant only
atoms, orbs = zip(*[(atom, norb) for atom, norb in norbs.items()])
# Make the kwant lattice
lat = kwant.lattice.general(lat_vecs, atom_coords, norbs=orbs)
# Store sublattices by name
sublattices = {
atom: sublat
for atom, sublat in zip(atoms, lat.sublattices)
}
sym = kwant.TranslationalSymmetry(*lat_vecs)
bulk = kwant.Builder(sym)
bulk[[sublattices['A'](0, 0), sublattices['B'](0, 0)]] = 0
def hop(site1, site2, c0):
return c0
bulk[lat.neighbors()] = hop
fsyst_family = kwant.wraparound.wraparound(syst_from_family).finalized()
fsyst_model = kwant.wraparound.wraparound(syst_from_model).finalized()
fsyst_kwant = kwant.wraparound.wraparound(bulk).finalized()
# Check that the energies are identical at random points in the Brillouin zone
coeff = 0.5 + np.random.rand()
for _ in range(20):
kx, ky = 3 * np.pi * (np.random.rand(2) - 0.5)
params = dict(c0=coeff, k_x=kx, k_y=ky)
hamiltonian1 = fsyst_kwant.hamiltonian_submatrix(params=params,
sparse=False)
hamiltonian2 = fsyst_family.hamiltonian_submatrix(params=params,
sparse=False)
assert allclose(hamiltonian1, hamiltonian2)
params = dict(g=coeff, k_x=kx, k_y=ky)
hamiltonian3 = fsyst_model.hamiltonian_submatrix(params=params,
sparse=False)
assert allclose(hamiltonian2, hamiltonian3)
# Include random onsites as well
one = sympy.numbers.One()
onsites = [
Model({one: np.array([[1, 0], [0, 0]])}, momenta=family[0].momenta),
Model({one: np.array([[0, 0], [0, 1]])}, momenta=family[0].momenta)
]
family = family + onsites
syst_from_family = model_to_builder(family,
norbs,
lat_vecs,
atom_coords,
coeffs=None)
gs = list(sympy.symbols('g0:%d' % 3, real=True))
ham = hamiltonian_from_family(family, coeffs=gs)
ham = Model(hamiltonian=ham, momenta=family[0].momenta)
syst_from_model = model_to_builder(ham, norbs, lat_vecs, atom_coords)
def onsite_A(site, c1):
return c1
def onsite_B(site, c2):
return c2
bulk[[sublattices['A'](0, 0)]] = onsite_A
bulk[[sublattices['B'](0, 0)]] = onsite_B
fsyst_family = kwant.wraparound.wraparound(syst_from_family).finalized()
fsyst_model = kwant.wraparound.wraparound(syst_from_model).finalized()
fsyst_kwant = kwant.wraparound.wraparound(bulk).finalized()
# Check equivalence of the Hamiltonian at random points in the BZ
coeffs = 0.5 + np.random.rand(3)
for _ in range(20):
kx, ky = 3 * np.pi * (np.random.rand(2) - 0.5)
params = dict(c0=coeffs[0], c1=coeffs[1], c2=coeffs[2], k_x=kx, k_y=ky)
hamiltonian1 = fsyst_kwant.hamiltonian_submatrix(params=params,
sparse=False)
hamiltonian2 = fsyst_family.hamiltonian_submatrix(params=params,
sparse=False)
assert allclose(hamiltonian1, hamiltonian2)
params = dict(g0=coeffs[0], g1=coeffs[1], g2=coeffs[2], k_x=kx, k_y=ky)
hamiltonian3 = fsyst_model.hamiltonian_submatrix(params=params,
sparse=False)
assert allclose(hamiltonian2, hamiltonian3)