AngularMomentum

class AngularMomentum(num_spatial_orbitals, overlap=None)

Bases: object

The AngularMomentum property.

The operator constructed by this property is the $S^2$ operator which is computed as:

\[S^2 = (S^+ S^- + S^- S^+) / 2 + S^z S^z\]

Warning

If you are working with a non-orthogonal basis, you _must_ provide the overlap attribute in order to obtain the correct expectation value of this observable. Refer to the more extensive documentation of the s_operators module for more details.

See also

• the $S^z$ operator: s_z_operator()

• the $S^+$ operator: s_plus_operator()

• the $S^-$ operator: s_minus_operator()

The following attributes can be set via the initializer but can also be read and updated once the AngularMomentum object has been constructed.

num_spatial_orbitals

the number of spatial orbitals.

Type:

int

Parameters:

• num_spatial_orbitals (int) – the number of spatial orbitals in the system.

• overlap (np.ndarray | None) – the overlap-matrix between the $alpha$- and $beta$-spin orbitals. When this is None, the overlap-matrix is assumed to be identity.

Attributes

overlap

The overlap-matrix between the $alpha$- and $beta$-spin orbitals.

When this is None, the overlap-matrix is assumed to be identity.

Methods

interpret(result)

Interprets an EigenstateResult in this property’s context.

Parameters:

result (qiskit_nature.second_q.problems.EigenstateResult) – the result to add meaning to.

second_q_ops()

Returns the second quantized angular momentum operator.

Returns:

A mapping of strings to FermionicOp objects.

Return type:

Mapping[str, FermionicOp]