kwant.system.
System
[source]¶Abstract general low-level system.
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.
The system graph.
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.
The names of the parameters on which the system depends. This attribute is provisional and may be changed in a future version of Kwant
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.
Positional arguments to pass to the hamiltonian
method. Mutually
exclusive with ‘params’.
Whether to return a sparse or a dense matrix. Defaults to False
.
Whether to return arrays of numbers of orbitals. Defaults to False
.
Dictionary of parameter names and their values. Mutually exclusive with ‘args’.
Submatrix of Hamiltonian of the system.
Numbers of orbitals on each site in to_sites. Only returned when
return_norb
is true.
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.