kwant.system.FiniteSystemMixin

class kwant.system.FiniteSystemMixin[source]

Bases: object

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.

Attributes
leadssequence of leads

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).

lead_interfacessequence of sequences of integers

Each sub-sequence contains the indices of the system sites to which the lead is connected.

lead_paddingssequence of sequences of integers

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.

parametersfrozenset of strings

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

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.

Parameters
energyfloat

Energy at which the modes or self-energies have to be evaluated.

argssequence

Additional parameters required for calculating the Hamiltionians. Deprecated in favor of ‘params’ (and mutually exclusive with it).

leadssequence of integers or None

Indices of the leads to be precalculated. If None, all are precalculated.

what‘modes’, ‘selfenergy’, ‘all’

The quantitity to precompute. ‘all’ will compute both modes and self-energies. Defaults to ‘modes’.

paramsdict, optional

Dictionary of parameter names and their values. Mutually exclusive with ‘args’.

Returns
systFiniteSystem

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’.

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