Examining now the electron-hole excitations on the level of the BSE, the reduction of the number of occupied orbitals limits the transitions used in the expansion of the two-particle wavefunctions to those starting from the active subsystem. Furthermore, different quasiparticle energies obtained at GW level directly affect the free transition term D vc,v ′ c ′ from Eq. ( ) in the BSE Hamiltonian. The exchange and direct (screened) terms of the electron-hole interaction kernel K x vc,v ′ c ′ and K d vc,v ′ c ′ are affected in similar ways from changes in the orbitals, energies, and screening as Σ x and Σ c , respectively. As a consequence of the reduced screening, a stronger electron-hole attraction can be expected compared to the full-system calculation. This stronger binding of electron and hole in turn compensates to some degree the increased quasiparticle gap entering the free transition term.