When optimizing the CI vectors of fragment basis functions, even though we use spin shuffle operations to guarantee that the final model space is spin-adapted, we still have to choose in what Sz sector for each fragment we optimize the CI vectors, because the fragments' spins interact with each other through a 1-electron operator. Currently, the choice is extremely arbitrary and difficult to even describe. A more systematic way of choosing the Sz space needs to be made in order for the method to be reproducible.
When optimizing the CI vectors of fragment basis functions, even though we use spin shuffle operations to guarantee that the final model space is spin-adapted, we still have to choose in what Sz sector for each fragment we optimize the CI vectors, because the fragments' spins interact with each other through a 1-electron operator. Currently, the choice is extremely arbitrary and difficult to even describe. A more systematic way of choosing the Sz space needs to be made in order for the method to be reproducible.