Explore the connection between Koopmans' theorem and the spectral potential in this 45-minute tutorial by Andrea Ferretti, part of the Advanced Quantum ESPRESSO series on Hubbard and Koopmans functionals from linear response. Delve into topics such as mass construction, screening coefficients, and technical details of the approach. Examine similar ideas, the GW100 benchmark set, and applications to large molecules. Investigate matrix elements, spectra, and photon energy considerations. Learn about extended systems, band gap studies, and local orbital-dependent functions. Understand the equipment theorem, particle approximations, and various potentials. Gain insights into this advanced quantum mechanical topic, with opportunities for questions and discussion at the conclusion.