e high quality and compactness of the CIPSI wave function was also used for quantum Monte Carlo calculations to characterize the ground state of the water and the FeS molecules, and obtained highly accurate excitation energies. Of course, the technical considerations were not the main concern of the di erent articles that were produced. Because the present work focused on the actual implementation of the methods at least as much as on the theory behind them, this article is a perfect opportunity to discuss in depth their implementation.