kwant.system.
FiniteSystem
[source]¶Abstract finite low-level system, possibly with leads.
Notes
The length of leads
must be equal to the length of lead_interfaces
and lead_paddings
.
For lead n
, the method leads[n].selfenergy must return a square matrix
whose size is sum(len(self.hamiltonian(site, site)) for site in
self.lead_interfaces[n])
. The output of leads[n].modes
has to be a
tuple of PropagatingModes
, StabilizedModes
.
Often, the elements of leads will be instances of InfiniteSystem
. If
this is the case for lead n
, the sites lead_interfaces[n]
match
the first len(lead_interfaces[n])
sites of the InfiniteSystem.
Each lead has to provide a method selfenergy
that has
the same signature as InfiniteSystem.selfenergy
(without the
self
parameter), and must have property parameters
:
a collection of strings that name the system parameters (
though this requirement is provisional and may be removed in
a future version of Kwant).
It may also provide modes
that has the
same signature as InfiniteSystem.modes
(without the self
parameter).
Each sub-sequence contains the indices of the system sites to which the lead is connected.
Each sub-sequence contains the indices of the system sites that belong to the lead, and therefore have the same onsite as the lead sites, and are connected by the same hoppings as the lead sites.
The names of the parameters on which the system depends. This does not include the parameters for any leads. 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.
precalculate
(energy=0, args=(), leads=None, what='modes', *, params=None)[source]¶Precalculate modes or self-energies in the leads.
Construct a copy of the system, with the lead modes precalculated, which may significantly speed up calculations where only the system is changing.
Energy at which the modes or self-energies have to be evaluated.
Additional parameters required for calculating the Hamiltionians. Deprecated in favor of ‘params’ (and mutually exclusive with it).
Numbers of the leads to be precalculated. If None
, all are
precalculated.
The quantitity to precompute. ‘all’ will compute both modes and self-energies. Defaults to ‘modes’.
Dictionary of parameter names and their values. Mutually exclusive with ‘args’.
A copy of the original system with some leads precalculated.
Notes
If the leads are precalculated at certain energy or args values, they might give wrong results if used to solve the system with different parameter values. Use this function with caution.
validate_symmetries
(args=(), *, params=None)[source]¶Check that the Hamiltonian satisfies discrete symmetries.
Applies validate
to the
Hamiltonian, see its documentation for details on the return
format.
Providing positional arguments via ‘args’ is deprecated, instead, provide named parameters as a dictionary via ‘params’.