Explore the design of auxiliary systems and connectors for spectroscopy in this comprehensive tutorial video from the Advanced Quantum ESPRESSO series. Delve into quantum mechanics, historical perspectives, and advanced concepts like the C1 Chain, inverse condition, and approximations. Learn about the connection framework, Green's function, and local density approximation. Examine alternative solutions, local spectral functions, and sound filter equations. Discover the advantages of exact exchange correlation potential with practical examples. Gain insights into spectra potential and its applications. Conclude with a summary and opportunity for questions, enhancing your understanding of Hubbard and Koopmans functionals from linear response.