Silicon & Germanium spin qubits have made outstanding progress in the past few years. In these devices, the elementary information is stored as a coherent superposition of the spin states of an electron or hole in a quantum dot. These spins can be manipulated electrically owing to spin-orbit coupling, and are entangled through exchange interactions, allowing for a variety of one- and two-qubit gates required for quantum computing and simulation. Grenoble is developing original spin qubit platforms on Si and Ge, and holds various records in spin lifetimes and spin-photon interactions. At CEA Grenoble, we support the progress of these advanced quantum technologies with state-of-the-art modelling. In particular, we are developing the TB_Sim code, able to describe very realistic qubit structures down to the atomic scale. The role of Coulomb interactions in spin qubits remains poorly understood. Quantum dots with 3 to 5 electrons or holes are expected to screen noise & disorder better than singly-occupied ones; yet Coulomb interactions can dramatically reshape the spectrum and dynamics of the system (Wigner localization…). The aim of this master training is, therefore, to model the effects of Coulomb interactions on spin qubits using “configuration interaction” methods for the many-body wave functions, in relation with ongoing experiments in the lab. This Master thesis may be followed by a PhD project on spin manipulation and entanglement in arrays of spin qubits.