qat.fermion.chemistry.ucc.get_cluster_ops

qat.fermion.chemistry.ucc.get_cluster_ops(n_electrons: int, nqbits: Optional[int] = None, noons: Optional[List[float]] = None) → List[FermionHamiltonian]

Compute the cluster operators.

Parameters

• n_electrons (int) – The number of active electrons of the system.

• nqbits (Optional[int]) – The number of qubits.

• noons (Optional[List[float]]) – The natural-orbital occupation numbers \(n_i\), sorted in descending order (from high occupations to low occupations) (doubled due to spin degeneracy).

Returns

The list of cluster operators \(\{i T_{a}^{i}, a \in \mathcal{I}', i \in \mathcal{O}' \} \cup \{iT_{ab}^{ij}, a>b, i>j, a,b \in \mathcal{I}', i,j \in \mathcal{O}'\}\), with \(\mathcal{I}\) (resp. \(\mathcal{O}\)) the inoccupied (resp. occupied) orbitals.

Return type

List[FermionHamiltonian]

Note

This function accepts as input the number of qubits or the noons. One of them is needed for the computation of the cluster operators. n_electrons and n_qbits must be even.