qat.fermion.chemistry.ucc.get_cluster_ops

qat.fermion.chemistry.ucc.get_cluster_ops(n_electrons: int, nqbits: int | None = None, noons: List[float] | None = 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 $\{i{T}_a^i,a\in {\mathcal{I}}^{\prime },i\in {\mathcal{O}}^{\prime }\}\cup \{i{T}_{ab}^{ij},a>b,i>j,a,b\in {\mathcal{I}}^{\prime },i,j\in {\mathcal{O}}^{\prime }\}$, 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.