FermionSite

• full name: tenpy.networks.site.FermionSite

• parent module: tenpy.networks.site

• type: class

Inheritance Diagram

Methods

FermionSite.__init__([conserve, filling])	Initialize self.
FermionSite.add_op(name, op[, need_JW, hc])	Add one on-site operators.
FermionSite.change_charge([new_leg_charge, …])	Change the charges of the site (in place).
FermionSite.from_hdf5(hdf5_loader, h5gr, subpath)	Load instance from a HDF5 file.
FermionSite.get_hc_op_name(name)	Return the hermitian conjugate of a given operator.
FermionSite.get_op(name)	Return operator of given name.
FermionSite.multiply_op_names(names)	Multiply operator names together.
FermionSite.op_needs_JW(name)	Whether an (composite) onsite operator is fermionic and needs a Jordan-Wigner string.
FermionSite.remove_op(name)	Remove an added operator.
FermionSite.rename_op(old_name, new_name)	Rename an added operator.
FermionSite.save_hdf5(hdf5_saver, h5gr, subpath)	Export self into a HDF5 file.
FermionSite.state_index(label)	Return index of a basis state from its label.
FermionSite.state_indices(labels)	Same as state_index(), but for multiple labels.
FermionSite.test_sanity()	Sanity check, raises ValueErrors, if something is wrong.
FermionSite.valid_opname(name)	Check whether ‘name’ labels a valid onsite-operator.

Class Attributes and Properties

FermionSite.dim	Dimension of the local Hilbert space.
FermionSite.onsite_ops	Dictionary of on-site operators for iteration.

class tenpy.networks.site.FermionSite(conserve='N', filling=0.5)

Bases: tenpy.networks.site.Site

Create a Site for spin-less fermions.

Local states are empty and full.

Warning

Using the Jordan-Wigner string (JW) is crucial to get correct results, otherwise you just describe hardcore bosons! Further details in Fermions and the Jordan-Wigner transformation.

operator	description
Id	Identity \(\mathbb{1}\)
JW	Sign for the Jordan-Wigner string.
C	Annihilation operator \(c\) (up to ‘JW’-string left of it)
Cd	Creation operator \(c^\dagger\) (up to ‘JW’-string left of it)
N	Number operator \(n= c^\dagger c\)
dN	\(\delta n := n - filling\)
dNdN	\((\delta n)^2\)

conserve	qmod	exluded onsite operators
'N'	[1]	–
'parity'	[2]	–
None	[]	–

Parameters

• conserve (str) – Defines what is conserved, see table above.

• filling (float) – Average filling. Used to define dN.

conserve

Defines what is conserved, see table above.

Type

str

filling

Average filling. Used to define dN.

Type

float

add_op(name, op, need_JW=False, hc=None)

Add one on-site operators.

Parameters

• name (str) – A valid python variable name, used to label the operator. The name under which op is added as attribute to self.

• op (np.ndarray | Array) – A matrix acting on the local hilbert space representing the local operator. Dense numpy arrays are automatically converted to Array. LegCharges have to be [leg, leg.conj()]. We set labels 'p', 'p*'.

• need_JW (bool) – Whether the operator needs a Jordan-Wigner string. If True, add name to need_JW_string.

• hc (None | False | str) – The name for the hermitian conjugate operator, to be used for hc_ops. By default (None), try to auto-determine it. If False, disable adding antries to hc_ops.

change_charge(new_leg_charge=None, permute=None)

Change the charges of the site (in place).

Parameters

• new_leg_charge (LegCharge | None) – The new charges to be used. If None, use trivial charges.

• permute (ndarray | None) – The permuation applied to the physical leg, which gets used to adjust state_labels and perm. If you sorted the previous leg with perm_qind, new_leg_charge = leg.sort(), use old_leg.perm_flat_from_perm_qind(perm_qind). Ignored if None.

property dim

Dimension of the local Hilbert space.

classmethod from_hdf5(hdf5_loader, h5gr, subpath)

Load instance from a HDF5 file.

This method reconstructs a class instance from the data saved with save_hdf5().

Parameters

• hdf5_loader (Hdf5Loader) – Instance of the loading engine.

• h5gr (Group) – HDF5 group which is represent the object to be constructed.

• subpath (str) – The name of h5gr with a '/' in the end.

Returns

obj – Newly generated class instance containing the required data.

Return type

cls

get_hc_op_name(name)

Return the hermitian conjugate of a given operator.

Parameters

name (str) – The name of the operator to be returned. Multiple operators separated by whitespace are interpreted as an operator product, exactly as get_op() does.

Returns

hc_op_name – Operator name for the hermi such that get_op() of

Return type

str

get_op(name)

Return operator of given name.

Parameters

name (str) – The name of the operator to be returned. In case of multiple operator names separated by whitespace, we multiply them together to a single on-site operator (with the one on the right acting first).

Returns

op – The operator given by name, with labels 'p', 'p*'. If name already was an npc Array, it’s directly returned.

Return type

np_conserved

multiply_op_names(names)

Multiply operator names together.

Join the operator names in names such that get_op returns the product of the corresponding operators.

Parameters

names (list of str) – List of valid operator labels.

Returns

combined_opname – A valid operator name Operatorname representing the product of operators in names.

Return type

str

property onsite_ops

Dictionary of on-site operators for iteration.

Single operators are accessible as attributes.

op_needs_JW(name)

Whether an (composite) onsite operator is fermionic and needs a Jordan-Wigner string.

Parameters

name (str) – The name of the operator, as in get_op().

Returns

needs_JW – Whether the operator needs a Jordan-Wigner string, judging from need_JW_string.

Return type

bool

remove_op(name)

Remove an added operator.

Parameters

name (str) – The name of the operator to be removed.

rename_op(old_name, new_name)

Rename an added operator.

Parameters

• old_name (str) – The old name of the operator.

• new_name (str) – The new name of the operator.

save_hdf5(hdf5_saver, h5gr, subpath)

Export self into a HDF5 file.

This method saves all the data it needs to reconstruct self with from_hdf5().

This implementation saves the content of __dict__ with save_dict_content(), storing the format under the attribute 'format'.

Parameters

• hdf5_saver (Hdf5Saver) – Instance of the saving engine.

• h5gr (:class`Group`) – HDF5 group which is supposed to represent self.

• subpath (str) – The name of h5gr with a '/' in the end.

state_index(label)

Return index of a basis state from its label.

Parameters

label (int | string) – eather the index directly or a label (string) set before.

Returns

state_index – the index of the basis state associated with the label.

Return type

int

state_indices(labels)

Same as state_index(), but for multiple labels.

test_sanity()

Sanity check, raises ValueErrors, if something is wrong.

valid_opname(name)

Check whether ‘name’ labels a valid onsite-operator.

Parameters

name (str) – Label for the operator. Can be multiple operator(labels) separated by whitespace, indicating that they should be multiplied together.

Returns

valid – True if name is a valid argument to get_op().

Return type

bool