def calc_n(H, q):
r""" General method to obtain the spin densities for periodic or finite systems at a given temperature
It obtains the spin densities from the direct diagonalization of the Hamiltonian (``H.H``) taking into account
a possible overlap matrix (``H.H.S``):
.. math::
\langle n_{i\sigma} \rangle = \sum_{\alpha}f_{\alpha\sigma}\sum_{j}c^{\alpha}_{i\sigma}c^{*\alpha}_{j\sigma}S_{ij}
Where :math:`f_{\alpha\sigma}` is the weight of eigenstate :math:`\alpha` for spin :math:`\sigma` at temperature ``kT`` (Fermi-Dirac distribution),
:math:`c^{\alpha}_{i\sigma}` are coefficients for eigenstate :math:`\alpha` with spin :math:`\sigma` represented in the basis of atomic orbitals
Parameters
----------
H: HubbardHamiltonian
`hubbard.HubbardHamiltonian` object of the system to obtain the spin-densities from
q: array_like
charge resolved in spin channels (first index for up-electrons and second index for down-electrons)
See Also
------------
sisl.physics.electron.EigenstateElectron.norm2: sisl routine to obtain the dot product of the eigenstates with the overlap matrix
"""
# Create fermi-level determination distribution
dist = sisl.get_distribution('fermi_dirac', smearing=H.kT)
Ef = H.H.fermi_level(H.mp, q=q, distribution=dist)
if not isinstance(Ef, (tuple, list, np.ndarray)):
Ef = np.array([Ef])
dist = [
sisl.get_distribution('fermi_dirac', smearing=H.kT, x0=Ef[s])
for s in range(H.spin_size)
]
ni = np.zeros((H.spin_size, H.sites))
Etot = 0
# Solve eigenvalue problems
def calc_occ(k, weight, spin):
n = np.empty_like(ni)
es = H.eigenstate(k, spin=spin)
# Reduce to occupied stuff
occ = es.occupation(dist[spin]) * weight
n = einsum('i,ij->j', occ, es.norm2(False).real)
Etot = es.eig.dot(occ)
# Return values
return n, Etot
# Loop k-points and weights
for w, k in zip(H.mp.weight, H.mp.k):
for s in range(H.spin_size):
n, etot = calc_occ(k, w, s)
ni[s] += n
Etot += etot
# Return spin densities and total energy
# if the Hamiltonian is not spin-polarized multiply Etot by 2 for spin degeneracy
return ni, (2. / H.spin_size) * Etot
def calc_n(H, q):
r""" General method to obtain the spin densities for periodic or finite systems at a given temperature
It obtains the spin densities from the direct diagonalization of the Hamiltonian (``H.H``) taking into account
a possible overlap matrix (``H.H.S``):
.. math::
\langle n_{i\sigma} \rangle = \sum_{\alpha}f_{\alpha\sigma}\sum_{j}c^{\alpha}_{i\sigma}c^{*\alpha}_{j\sigma}S_{ij}
Where :math:`f_{\alpha\sigma}` is the weight of eigenstate :math:`\alpha` for spin :math:`\sigma` at temperature ``kT`` (Fermi-Dirac distribution),
:math:`c^{\alpha}_{i\sigma}` are coefficients for eigenstate :math:`\alpha` with spin :math:`\sigma` represented in the basis of atomic orbitals
Parameters
----------
H: HubbardHamiltonian
`hubbard.HubbardHamiltonian` object of the system to obtain the spin-densities from
q: array_like
charge resolved in spin channels (first index for up-electrons and second index for down-electrons)
See Also
------------
sisl.physics.electron.EigenstateElectron.norm2: sisl routine to obtain the dot product of the eigenstates with the overlap matrix
"""
# Create fermi-level determination distribution
dist = sisl.get_distribution('fermi_dirac', smearing=H.kT)
Ef = H.H.fermi_level(H.mp, q=q, distribution=dist)
dist_up = sisl.get_distribution('fermi_dirac', smearing=H.kT, x0=Ef[0])
dist_dn = sisl.get_distribution('fermi_dirac', smearing=H.kT, x0=Ef[1])
ni = np.zeros((2, H.sites))
Etot = 0
# Solve eigenvalue problems
def calc_occ(k, weight):
n = np.empty_like(ni)
es_up = H.eigenstate(k, spin=0)
es_dn = H.eigenstate(k, spin=1)
# Reduce to occupied stuff
occ_up = es_up.occupation(dist_up) * weight
n[0] = einsum('i,ij->j', occ_up, es_up.norm2(False).real)
occ_dn = es_dn.occupation(dist_dn) * weight
n[1] = einsum('i,ij->j', occ_dn, es_dn.norm2(False).real)
Etot = es_up.eig.dot(occ_up) + es_dn.eig.dot(occ_dn)
# Return values
return n, Etot
# Loop k-points and weights
for w, k in zip(H.mp.weight, H.mp.k):
n, etot = calc_occ(k, w)
ni += n
Etot += etot
return ni, Etot
def fermi_level(self, q=[None, None], dist='fermi_dirac'):
""" Find the fermi level for a certain charge `q` at a certain `kT`
Parameters
----------
q: array_like, optional
charge per spin channel. First index for spin up, second index for dn
dist: str or sisl.distribution, optional
distribution function
See Also
------------
sisl.physics.Hamiltonian.fermi_level : sisl class function
Returns
-------
Ef: numpy.array
Fermi-level for each spin channel
"""
Q = 1 * q
for i in (0, 1):
if Q[i] is None:
Q[i] = self.q[i]
if isinstance(dist, str):
dist = sisl.get_distribution(dist, smearing=self.kT)
Ef = self.H.fermi_level(self.mp, q=Q, distribution=dist)
return Ef
def fermi_level(self, q=[None, None], distribution='fermi_dirac'):
""" Find the fermi level for a certain charge `q` at a certain `kT`
Parameters
----------
q: array_like, optional
charge per spin channel. First index for spin up, second index for dn
If the Hamiltonian is unpolarized q should have only one component
otherwise it will take the first one
distribution: str or sisl.distribution, optional
distribution function
See Also
------------
sisl.physics.Hamiltonian.fermi_level : sisl class function
Returns
-------
Ef: numpy.array
Fermi-level for each spin channel
"""
Q = 1 * q
for i in range(self.spin_size):
if Q[i] is None:
Q[i] = self.q[i]
if isinstance(distribution, str):
distribution = sisl.get_distribution(distribution, smearing=self.kT)
Ef = self.H.fermi_level(self.mp, q=Q, distribution=distribution)
return Ef
def PDOS(self, egrid, eta=1e-3, spin=[0, 1], dist='Lorentzian', eref=0.):
""" Obtains the projected density of states (PDOS) of the system with a distribution function
Parameters
----------
egrid: array_like
Energy grid at which the DOS will be calculated.
eta: float, optional
Smearing parameter
spin: int, optional
If spin=0(1) it calculates the DOS for up (down) electrons in the system.
If spin is not specified it returns DOS_up + DOS_dn.
dist: str or sisl.distribution, optional
distribution for the convolution, defaults to Lorentzian
eref: float, optional
energy reference, defaults to zero
See Also
------------
sisl.get_distribution: sisl method to create distribution function
sisl.physics.electron.PDOS: sisl method to obtain PDOS
Returns
-------
PDOS: numpy.ndarray
projected density of states at the given energies for the selected spin
"""
# Ensure spin is iterable
if not isinstance(spin, (list, np.ndarray)):
spin = [spin]
# Check if egrid is numpy.ndarray
if not isinstance(egrid, np.ndarray):
egrid = np.array(egrid)
if isinstance(dist, str):
dist = sisl.get_distribution(dist, smearing=eta)
else:
warnings.warn(
"Using distribution created outside this function. The energy reference may be shifted if the distribution is calculated with respect to a non-zero energy value"
)
# Obtain PDOS
pdos = 0
for ispin in spin:
ev, evec = self.eigh(eigvals_only=False, spin=ispin)
ev -= eref
pdos += sisl.physics.electron.PDOS(egrid,
ev,
evec.T,
distribution=dist)
return pdos
def test_wrap_oplist(self, setup):
R, param = [0.1, 1.5], [1, 2.1]
H = Hamiltonian(setup.g.copy())
H.construct([R, param])
bz = MonkhorstPack(H, [10, 10, 1])
E = np.linspace(-4, 4, 1000)
dist = get_distribution('gaussian', smearing=0.05)
def wrap(es, parent, k, weight):
DOS = es.DOS(E, distribution=dist)
PDOS = es.PDOS(E, distribution=dist)
vel = es.velocity() * es.occupation().reshape(-1, 1)
return oplist([DOS, PDOS, vel])
bz.asaverage()
results = bz.eigenstate(wrap=wrap)
assert np.allclose(bz.DOS(E, distribution=dist), results[0])
assert np.allclose(bz.PDOS(E, distribution=dist), results[1])
def __init__(self,
HubbardHamiltonian,
k=[0, 0, 0],
spin=0,
direction=[1, 0, 0],
origo=[0, 0, 0],
projection='2D',
nx=601,
gamma_x=0.5,
dx=5.0,
dist_x='gaussian',
ne=501,
gamma_e=0.05,
emax=10.,
dist_e='lorentzian',
vmin=0,
vmax=None,
scale='linear',
**kwargs):
super().__init__(**kwargs)
ev, evec = HubbardHamiltonian.eigh(k=k, eigvals_only=False, spin=spin)
ev -= HubbardHamiltonian.find_midgap()
xyz = np.array(HubbardHamiltonian.geometry.xyz[:])
# coordinates relative to selected origo
xyz -= np.array(origo).reshape(1, 3)
# distance along projection axis
unitvec = np.array(direction)
unitvec = unitvec / unitvec.dot(unitvec)**0.5
coord = xyz.dot(unitvec)
xmin, xmax = min(coord) - dx, max(coord) + dx
emin, emax = -emax, emax
# Broaden along real-space axis
x = np.linspace(xmin, xmax, nx)
dist_x = sisl.get_distribution(dist_x, smearing=gamma_x)
xcoord = x.reshape(-1, 1) - coord.reshape(1, -1) # (nx, natoms)
if projection.upper() == '1D':
# distance perpendicular to projection axis
perp = xyz - coord.reshape(-1, 1) * unitvec
perp = np.einsum('ij,ij->i', perp, perp)
xcoord = (xcoord**2 + perp)**0.5
DX = dist_x(xcoord)
# Broaden along energy axis
e = np.linspace(emin, emax, ne)
dist_e = sisl.get_distribution(dist_e, smearing=gamma_e)
DE = dist_e(e.reshape(-1, 1) - ev.reshape(1, -1)) # (ne, norbs)
# Compute DOS
prob_dens = np.abs(evec)**2
DOS = DX.dot(prob_dens).dot(DE.T)
intdat = np.sum(DOS) * (x[1] - x[0]) * (e[1] - e[0])
print('Integrated LDOS spectrum (states within plot):', intdat,
DOS.shape)
cm = plt.cm.hot
if scale == 'log':
if vmin == 0:
vmin = 1e-4
norm = colors.LogNorm(vmin=vmin)
else:
# Linear scale
norm = colors.Normalize(vmin=vmin)
self.imshow = self.axes.imshow(DOS.T, extent=[xmin, xmax, emin, emax], cmap=cm, \
origin='lower', norm=norm, vmax=vmax)
title = f'LDOS projection in {projection.upper()}'
if projection.upper() == '1D':
title += r': origo [%.2f,%.2f,%.2f] (\AA)' % tuple(origo)
self.set_title(title)
self.set_xlabel(r'distance along [%.2f,%.2f,%.2f] (\AA)' %
tuple(direction))
self.set_ylabel(r'$E-E_\mathrm{midgap}$ (eV)')
self.set_xlim(xmin, xmax)
self.set_ylim(emin, emax)
self.axes.set_aspect('auto')
def __init__(self, Hdev, elec_SE, elec_idx, CC=None, V=0, **kwargs):
""" Initialize NEGF class """
# Global charge neutral reference energy (conveniently named fermi)
self.Ef = 0.
self.kT = Hdev.kT
self.eta = 0.1
# Immediately retrieve the distribution
dist = sisl.get_distribution('fermi_dirac', smearing=self.kT)
if not CC:
CC = os.path.split(__file__)[0] + "/EQCONTOUR"
# Extract weights and energy points from CC
contour_weight = sisl.io.tableSile(CC).read_data()
self.CC_eq = np.array([contour_weight[0] + 1j * contour_weight[1]])
self.w_eq = (contour_weight[2] + 1j * contour_weight[3]) / np.pi
self.NEQ = V != 0
self.mu = np.zeros(len(elec_SE))
if self.NEQ:
# in case the user has WBL electrodes
self.mu[0] = V * 0.5
self.mu[1] = -V * 0.5
# Define equilibrium contours
self.CC_eq = np.array(
[self.CC_eq[0] + self.mu[0], self.CC_eq[0] + self.mu[1]])
# Integration path for the non-Eq window
dE = 0.01
self.CC_neq = np.arange(
min(self.mu) - 5 * self.kT,
max(self.mu) + 5 * self.kT + dE, dE) + 1j * 0.001
# Weights for the non-Eq integrals
w_neq = dE * (dist(self.CC_neq.real - self.mu[0]) -
dist(self.CC_neq.real - self.mu[1]))
# Store weights for calculation of DELTA_L [0] and DELTA_R [1]
self.w_neq = np.array([w_neq, -w_neq]) / _pi
else:
self.CC_neq = np.array([])
def convert2SelfEnergy(elec_SE, mu):
if isinstance(elec_SE, (tuple, list)):
# here HH *must* be a HubbardHamiltonian (otherwise it will probably crash)
HH, semi_inf = elec_SE
Ef_elec = HH.fermi_level(q=HH.q, distribution=dist)
# Shift each electrode with its Fermi-level and chemical potential
# Since the electrodes are *bulk* i.e. the entire electronic structure
# is simply shifted
HH.shift(-Ef_elec + mu)
return sisl.RecursiveSI(HH.H, semi_inf)
# If elec_SE is already a SelfEnergy instance
# this will work since SelfEnergy instances overloads unknown attributes
# to the parent.
# This will only shift the electronic structure of the RecursiveSI.spgeom0
# and not RecursiveSI.spgeom1. However, for orthogonal basis, this is equivalent.
# TODO this should be changed when non-orthogonal basis' are used
try:
elec_SE.shift(mu)
except:
# the parent does not have the shift method
pass
return elec_SE
# convert all matrices to a sisl.SelfEnergy instance
self.elec_SE = list(map(convert2SelfEnergy, elec_SE, self.mu))
self.elec_idx = [np.array(idx).reshape(-1, 1) for idx in elec_idx]
# Ensure commensurate shapes
for SE, idx in zip(self.elec_SE, self.elec_idx):
assert len(SE) == len(idx)
# For a bias calcualtion, ensure that only the first
# two electrodes are RecursiveSI (all others should be WideBandSE)
if self.NEQ:
for i in range(2):
assert isinstance(self.elec_SE[i], sisl.RecursiveSI)
for i in range(2, len(self.elec_SE)):
assert isinstance(self.elec_SE[i], sisl.WideBandSE)
# In case all self-energies are WB, then we can change the eta value
if all(map(lambda obj: isinstance(obj, sisl.WideBandSE),
self.elec_SE)):
# The wide-band limit ensures that all electrons comes at a constant rate per
# energy.
# Although this *could* potentially be too high, then I think it should be ok
# since the electrodes more govern the DOS.
self.eta = 1.
# spin, electrode
self._ef_SE = _nested_list(2, len(self.elec_SE))
# spin, EQ-contour, energy, electrode
self._cc_eq_SE = _nested_list(Hdev.spin_size, *self.CC_eq.shape,
len(self.elec_SE))
# spin, energy, electrode
self._cc_neq_SE = _nested_list(Hdev.spin_size, self.CC_neq.shape[0],
len(self.elec_SE))
for i, se in enumerate(self.elec_SE):
for spin in range(Hdev.spin_size):
# Map self-energy at the Fermi-level of each electrode into the device region
self._ef_SE[spin][i] = se.self_energy(1j * self.eta, spin=spin)
for cc_eq_i, CC_eq in enumerate(self.CC_eq):
for ic, cc in enumerate(CC_eq):
# Do it also for each point in the CC, for all EQ CC
self._cc_eq_SE[spin][cc_eq_i][ic][i] = se.self_energy(
cc, spin=spin)
if self.NEQ:
for ic, cc in enumerate(self.CC_neq):
# And for each point in the Neq CC
self._cc_neq_SE[spin][ic][i] = se.self_energy(
cc, spin=spin)
# Build zigzag GNR
ZGNR = sisl.geom.zgnr(2)
# and 3NN TB Hamiltonian
H_elec = sp2(ZGNR, t1=2.7, t2=0.2, t3=0.18)
# Hubbard Hamiltonian of elecs
MFH_elec = HubbardHamiltonian(H_elec, U=U, nkpt=[102, 1, 1], kT=kT)
# Initialize spin densities
MFH_elec.set_polarization([0], dn=[-1]) # Ensure we break symmetry
# Converge Electrode Hamiltonians
dn = MFH_elec.converge(density.calc_n,
mixer=sisl.mixing.PulayMixer(weight=.7, history=7),
tol=1e-10)
dist = sisl.get_distribution('fermi_dirac', smearing=kT)
Ef_elec = MFH_elec.H.fermi_level(MFH_elec.mp, q=MFH_elec.q, distribution=dist)
print("Electrode Ef = ", Ef_elec)
# Shift each electrode with its Fermi-level and write it to netcdf file
MFH_elec.H.shift(-Ef_elec)
MFH_elec.H.write('MFH_elec.nc')
# Central region is a repetition of the electrodes without PBC
HC = H_elec.tile(3, axis=0)
HC.set_nsc([1, 1, 1])
# Map electrodes in the device region
elec_indx = [range(len(H_elec)), range(-len(H_elec), 0)]
# MFH object
MFH_HC = HubbardHamiltonian(HC.H, n=np.tile(MFH_elec.n, 3), U=U, kT=kT)
def __init__(self,
HH,
E,
sites=[],
spin=[0, 1],
ext_geom=None,
realspace=False,
eta=1e-3,
distribution='lorentzian',
**kwargs):
# Set default kwargs
if realspace:
if 'facecolor' not in kwargs:
kwargs['facecolor'] = 'None'
if 'cmap' not in kwargs:
kwargs['cmap'] = 'Greys'
else:
if 'cmap' not in kwargs:
kwargs['cmap'] = plt.cm.bwr
super().__init__(HH.geometry, ext_geom=ext_geom, **kwargs)
x = HH.geometry[:, 0]
y = HH.geometry[:, 1]
if realspace:
if 'shape' not in kwargs:
kwargs['shape'] = [100, 100, 1]
if 'vmin' not in kwargs:
kwargs['vmin'] = 0
xmin, xmax, ymin, ymax = self.xmin, self.xmax, self.ymin, self.ymax
if 'sc' not in kwargs:
if 'z' in kwargs:
origin = [xmin, ymin, -kwargs['z']]
else:
raise ValueError(
'Either a SC or the z coordinate to slice the real space grid needs to be passed'
)
kwargs['sc'] = sisl.SuperCell([xmax - xmin, ymax - ymin, 1000],
origin=origin)
if 'axis' not in kwargs:
kwargs['axis'] = 2
grid = 0
for s in spin:
ev, evec = HH.eigh(spin=s, eigvals_only=False)
if 'energy_window' in kwargs:
energy_window = kwargs['energy_window']
window_states = np.where(np.abs(ev - E) < energy_window)[0]
else:
window_states = range(HH.sites)
# Computing grids for all states is too slow... Let's use a window
energy_window = np.where(np.abs(ev - E) < 1.5)[0]
for ni in window_states:
v = evec[:, ni]
grid_n = real_space_grid(self.geometry,
kwargs['sc'],
v,
kwargs['shape'],
mode='wavefunction')
f = sisl.get_distribution(distribution,
smearing=eta,
x0=ev[ni])
weight = f(E)
# Slice it to obtain a 2D grid
slice_grid = grid_n.swapaxes(kwargs['axis'], 2).grid[:, :,
0].T
grid += (slice_grid.real**2 + slice_grid.imag**2) * weight
self.__realspace__(grid, **kwargs)
self.imshow.set_cmap(plt.cm.afmhot)
else:
pdos = HH.PDOS(E, eta=eta, spin=spin, dist=distribution)
self.axes.scatter(x, y, pdos, 'b')
for i, s in enumerate(sites):
self.axes.text(x[s], y[s], '%i' % i, fontsize=15, color='r')
