Create a singlet UCCSD generator for a system with n_electrons

This function generates a FermionOperator for a UCCSD generator designed to act on a single reference state consisting of n_qubits spin orbitals and n_electrons electrons, that is a spin singlet operator, meaning it conserves spin.

packed_amplitudes(list): List storing the unique single and double excitation amplitudes for a singlet UCCSD operator. The ordering lists unique single excitations before double excitations. n_qubits(int): Number of spin-orbitals used to represent the system, which also corresponds to number of qubits in a non-compact map. n_electrons(int): Number of electrons in the physical system. anti_hermitian(Bool): Flag to generate only normal CCSD operator rather than unitary variant, primarily for testing

generator(FermionOperator): Generator of the UCCSD operator that builds the UCCSD wavefunction.