kwant.system.System[source]¶Bases: object
Abstract general low-level system.
site_ranges[source]¶If provided, encodes ranges of sites that have the same number of
orbitals. Each triple consists of (first_site, norbs, orb_offset):
the first site in the range, the number of orbitals on each site in the
range, and the offset of the first orbital of the first site in the
range. In addition, the final triple should have the form
(graph.num_nodes, 0, tot_norbs) where tot_norbs is the
total number of orbitals in the system.
None or sorted sequence of triples of integers
parameters[source]¶The names of the parameters on which the system depends. This attribute is provisional and may be changed in a future version of Kwant
frozenset of strings
Notes
The sites of the system are indexed by integers ranging from 0 to
self.graph.num_nodes - 1.
Optionally, a class derived from System can provide a method
pos which is assumed to return the real-space position of a site
given its index.
Due to the ordering semantics of sequences, and the fact that a given
first_site can only appear at most once in site_ranges,
site_ranges is ordered according to first_site.
Consecutive elements in site_ranges are not required to have different
numbers of orbitals.
Methods
discrete_symmetry(args, *, params=None)[source]¶Return the discrete symmetry of the system.
Providing positional arguments via ‘args’ is deprecated, instead, provide named parameters as a dictionary via ‘params’.
hamiltonian(i, j, *args, params=None)[source]¶Return the hamiltonian matrix element for sites i and j.
If i == j, return the on-site Hamiltonian of site i.
if i != j, return the hopping between site i and j.
Hamiltonians may depend (optionally) on positional and keyword arguments.
Providing positional arguments via ‘args’ is deprecated, instead, provide named parameters as a dictionary via ‘params’.
hamiltonian_submatrix(self, args=(), to_sites=None, from_sites=None, sparse=False, return_norb=False, *, params=None)[source]¶Return a submatrix of the system Hamiltonian.
args (tuple, defaults to empty) – Positional arguments to pass to the hamiltonian method. Mutually
exclusive with ‘params’.
to_sites (sequence of sites or None (default)) –
from_sites (sequence of sites or None (default)) –
sparse (bool) – Whether to return a sparse or a dense matrix. Defaults to False.
return_norb (bool) – Whether to return arrays of numbers of orbitals. Defaults to False.
params (dict, optional) – Dictionary of parameter names and their values. Mutually exclusive with ‘args’.
hamiltonian_part (numpy.ndarray or scipy.sparse.coo_matrix) – Submatrix of Hamiltonian of the system.
to_norb (array of integers) – Numbers of orbitals on each site in to_sites. Only returned when
return_norb is true.
from_norb (array of integers) – Numbers of orbitals on each site in from_sites. Only returned when
return_norb is true.
Notes
The returned submatrix contains all the Hamiltonian matrix elements
from from_sites to to_sites. The default for from_sites and
to_sites is None which means to use all sites of the system in the
order in which they appear.