TermList¶

full name: tenpy.networks.terms.TermList
parent module: tenpy.networks.terms
type: class

Inheritance Diagram

Methods

`TermList.__init__`(terms[, strength])	Initialize self.
`TermList.from_hdf5`(hdf5_loader, h5gr, subpath)	Load instance from a HDF5 file.
`TermList.from_lattice_locations`(lattice, terms)	Initialize from a list of terms given in lattice indices instead of MPS indices.
`TermList.order_combine`(sites)	Order and combine operators in each term.
`TermList.save_hdf5`(hdf5_saver, h5gr, subpath)	Export self into a HDF5 file.
`TermList.to_OnsiteTerms_CouplingTerms`(sites)	Convert to `OnsiteTerms` and `CouplingTerms`

class tenpy.networks.terms.TermList(terms, strength=1.0)[source]¶

Bases: tenpy.tools.hdf5_io.Hdf5Exportable

A list of terms (=operator names and sites they act on) and associated strengths.

A representation of terms, similar as OnsiteTerms, CouplingTerms and MultiCouplingTerms.

This class does not store operator strings between the sites. Jordan-Wigner strings of fermions are added during conversion to (Multi)CouplingTerms.

Parameters

terms (list of list of (str, int)) – List of terms where each term is a list of tuples (opname, i) of an operator name and a site i it acts on. For Fermions, the order is the order in the mathematic sense, i.e., the right-most/last operator in the list acts last.
strengths ((list of) float/complex) – For each term in terms an associated prefactor or strength. A single number holds for all terms equally.

terms¶

List of terms where each term is a tuple (opname, i) of an operator name and a site i it acts on.

Type: list of list of (str, int)

strengths¶

For each term in terms an associated prefactor or strength.

Type: 1D ndarray

Examples

For fermions, the term \(0.5(c^\dagger_0 c_2 + h.c.) + 1.3 * n_1\) can be represented by:

>>> t = TermList([[('Cd', 0), ('C', 2)], [('Cd', 2), ('C', 0)], [('N', 1)]],
...              [0.5,                   0.5,                   1.3])
>>> print(t)
0.50000 * Cd_0 C_2 +
0.50000 * Cd_2 C_0 +
1.30000 * N_1

If you have a Lattice, you might also want to specify the location of the operators by lattice indices insted of MPS indices. For example, you can obtain the nearest-neighbor density terms without double counting each pair) on a TriangularLattice:

>>> lat = tenpy.models.lattice.Triangular(6, 6, None, bc_MPS='infinite', bc='periodic')
>>> t2_terms = [[('N', [0, 0, u1]), ('N', [dx[0], dx[1], u2])]
...             for (u1, u2, dx) in lat.pairs['nearest_neighbors']]
>>> t2 = TermList.from_lattice_locations(lat, t2_terms)
>>> print(t2)
1.00000 * N_0 N_6 +
1.00000 * N_0 N_-5 +
1.00000 * N_0 N_5

The negative index -5 here indicates a tensor left of the current MPS unit cell.

classmethod from_lattice_locations(lattice, terms, strength=1.0, shift=None)[source]¶

Initialize from a list of terms given in lattice indices instead of MPS indices.

Parameters

lattice (Lattice) – The underlying lattice to be used for conversion, e.g. M.lat from a Model.
terms (list of list of (str, tuple)) – List of terms, where each term is a tuple (opname, lat_idx) with lat_idx itself being a tuple (x, y, u) (for a 2D lattice) of the lattice corrdinates.
strengths ((list of) float/complex) – For each term in terms an associated prefactor or strength. A single number holds for all terms equally.
shift (None | tuple of int) – Overall shift added to all lattice coordinates lat_idx in terms before conversion. None defaults to no shift.

Returns

term_list – Representation of the terms.

Return type

TermList

to_OnsiteTerms_CouplingTerms(sites)[source]¶

Convert to OnsiteTerms and CouplingTerms

Performs Jordan-Wigner transformation for fermionic operators.

Parameters

sites (list of Site) – Defines the local Hilbert space for each site. Used to check whether the operators need Jordan-Wigner strings. The length is used as L for the onsite_terms and coupling_terms.

Returns

onsite_terms (OnsiteTerms) – Onsite terms.
coupling_terms (CouplingTerms | MultiCouplingTerms) – Coupling terms. If self contains terms involving more than two operators, a MultiCouplingTerms instance, otherwise just CouplingTerms.

order_combine(sites)[source]¶

Order and combine operators in each term.

Parameters: sites (list of Site) – Defines the local Hilbert space for each site. Used to check whether the operators anticommute (= whether they need Jordan-Wigner strings) and for multiplication rules.