FermionSite

• full name: tenpy.networks.site.FermionSite

• parent module: tenpy.networks.site

• type: class

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

conservestr

Defines what is conserved, see table above.

fillingfloat

Average filling. Used to define dN.

Attributes

conservestr

Defines what is conserved, see table above.

fillingfloat

Average filling. Used to define dN.

Methods

add_op(self, name, op[, need_JW])	Add one on-site operators.
change_charge(self[, new_leg_charge, permute])	Change the charges of the site (in place).
get_op(self, name)	Return operator of given name.
multiply_op_names(self, names)	Multiply operator names together.
op_needs_JW(self, name)	Whether an (composite) onsite operator is fermionic and needs a Jordan-Wigner string.
remove_op(self, name)	Remove an added operator.
rename_op(self, old_name, new_name)	Rename an added operator.
state_index(self, label)	Return index of a basis state from its label.
state_indices(self, labels)	Same as state_index(), but for multiple labels.
test_sanity(self)	Sanity check, raises ValueErrors, if something is wrong.
valid_opname(self, name)	Check whether ‘name’ labels a valid onsite-operator.

add_op(self, name, op, need_JW=False)

Add one on-site operators.

Parameters

namestr

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

opnp.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_JWbool

Whether the operator needs a Jordan-Wigner string. If True, the function adds name to need_JW_string.

change_charge(self, new_leg_charge=None, permute=None)

Change the charges of the site (in place).

Parameters

new_leg_chargeLegCharge | None

The new charges to be used. If None, use trivial charges.

permutendarray | 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 leg.perm_flat_from_perm_qind(perm_qind). Ignored if None.

property dim

Dimension of the local Hilbert space.

get_op(self, name)

Return operator of given name.

Parameters

namestr

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

opnp_conserved

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

multiply_op_names(self, names)

Multiply operator names together.

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

Parameters

nameslist of str

List of valid operator labels.

Returns

combined_opnamestr

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

property onsite_ops

Dictionary of on-site operators for iteration.

Single operators are accessible as attributes.

op_needs_JW(self, name)

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

Parameters

namestr

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

Returns

needs_JWbool

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

remove_op(self, name)

Remove an added operator.

Parameters

namestr

The name of the operator to be removed.

rename_op(self, old_name, new_name)

Rename an added operator.

Parameters

old_namestr

The old name of the operator.

new_namestr

The new name of the operator.

state_index(self, label)

Return index of a basis state from its label.

Parameters

labelint | string

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

Returns

state_indexint

the index of the basis state associated with the label.

state_indices(self, labels)

Same as state_index(), but for multiple labels.

test_sanity(self)

Sanity check, raises ValueErrors, if something is wrong.

valid_opname(self, name)

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

Parameters

namestr

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

Returns

validbool

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