The Theory and Simulation group (TheoSim) specializes in the use and development of theoretical chemistry tools for the study of physico-chemical systems. Thanks to our broad expertise, we design and distribute codes, tools, and models within the international community, enabling the study of chemical and biological phenomena at atomic and molecular scales. Our research is organized around three main areas: photochemistry and spectroscopy, the study of elementary processes induced by ionizing radiation, and the modeling of biological systems. We focus on a wide range of systems, from isolated molecules to complex biomolecules, including species in solution, crystalline structures, and nano-objects. Our work is primarily fundamental research, while also integrating into experimental projects carried out within the ICP or in collaboration with external partners, covering a wide range of applications.