ffsim.MolecularHamiltonianSpinless¶

class ffsim.MolecularHamiltonianSpinless(one_body_tensor, two_body_tensor, constant=0.0)[source]¶

A spinless molecular Hamiltonian.

A Hamiltonian of the form

\[H = \sum_{pq} h_{pq} a^\dagger_{p} a_{q} + \frac12 \sum_{pqrs} h_{pqrs} a^\dagger_{p} a^\dagger_{r} a_{s} a_{q} + \text{constant}.\]

Here \(h_{pq}\) is called the one-body tensor and \(h_{pqrs}\) is called the two-body tensor.

Attributes

Methods

`from_fermion_operator`(op)	Initialize a MolecularHamiltonianSpinless from a FermionOperator.
`rotated`(orbital_rotation)	Return the Hamiltonian in a rotated orbital basis.

static from_fermion_operator(op)[source]¶

Initialize a MolecularHamiltonianSpinless from a FermionOperator.

The input operator must contain only terms of the following form:

Any other terms will cause an error to be raised. No attempt will be made to normal-order terms.

Since the Hamiltonian is spinless, the fermionic actions in the input operator must all carry the spin alpha label (see cre_a() and des_a()).

Parameters:: op (FermionOperator) – The FermionOperator from which to initialize the Hamiltonian.
Return type:: MolecularHamiltonianSpinless
Returns:: The MolecularHamiltonianSpinless represented by the input FermionOperator.

rotated(orbital_rotation)[source]¶

Return the Hamiltonian in a rotated orbital basis.

Given an orbital rotation \(\mathcal{U}\), returns the operator

\[\mathcal{U} H \mathcal{U}^\dagger\]

where \(H\) is the original Hamiltonian.