Ground-state study of a donor–acceptor model with finite charge-transfer energy

A donor–acceptor model with randomly distributed N donor and N acceptor sites and with finite charge transfer energy Δ is investigated at zero temperature by means of computer simulations on two-dimensional samples of different sizes. We demonstrate that the density of one-electron excitations g( ε) for acceptors in the vicinity of the Fermi energy μ depends essentially on the size of the sample investigated and that g( ε) further away from μ exhibits a size-independent power-law with the non-universal exponent decreasing with increasing Δ. Rigorous relations for μ and for the mapping of g( ε) for donors into g( ε) for acceptors are also given.