Fig. shows that for the 3 A , 1 A transition, there is no rotation of hole and particle orbitals, giving rise to a weak coupling. Note a similarity between the holes and particles: there is no change in orbital shape, and these two states can be represented well by spin-adapted configurations of two open-shell determinants constructed from the respective NTOs. There is always a sign change in these combinations, coming from the Clebsh-Gordon coefficients, which can be observed in one of the NTO pairs for ( 3 A , 1 A ), because singular value decomposition preserves phases.