  We demonstrate that the effective Hamiltonians obtained with the downfolding
procedure based on double unitary coupled cluster (DUCC) ansatz can be used in
the context of Greens function coupled cluster (GFCC) formalism to calculate
spectral functions of molecular systems. This combined approach (DUCC-GFCC)
provides a significant reduction of numerical effort and good agreement with
the corresponding all-orbital GFCC methods in energy windows that are
consistent with the choice of active space. These features are demonstrated on
the example of two benchmark systems: H2O and N2, where DUCC-GFCC calculations
were performed for active spaces of various sizes.
