ffsim.ccsd_generator_unrestricted

ffsim.ccsd_generator_unrestricted(t1, t2)[source]

Unrestricted coupled cluster, singles and doubles (CCSD) generator.

The restricted CCSD generator is

\[T = T_1 + T_2\]

where \(T_1\) is the unrestricted singles excitations operator (see singles_excitations_unrestricted()) and \(T_2\) is the restricted doubles excitations operator (see doubles_excitations_unrestricted()).

Parameters:

  • t1 (tuple[ndarray, ndarray]) – The singles amplitudes. This should be a pair of Numpy arrays, (t1a, t1b), containing the spin-up and spin-down singles amplitudes. t1a should have shape (nocc_a, nvrt_a), where nocc_a is the number of occupied spin-up orbitals and nvrt_a is the number of virtual spin-up orbitals. t1b should have shape (nocc_b, nvrt_b), where nocc_b is the number of occupied spin-down orbitals and nvrt_b is the number of virtual spin-down orbitals.

  • t2 (tuple[ndarray, ndarray, ndarray]) – The doubles amplitudes. This should be a tuple of three of Numpy arrays, (t2aa, t2ab, t2bb).

Return type:

FermionOperator

Returns:

The CCSD generator.