• ab initio
• cavity
• magnetic effects
• qubit
• spin
• strong coupling

Efficient spin engineering procedures are essential to control several basic processes in quantum computation, spectroscopy and photochemistry.
However, a fine control of spin properties is usually challenging in standard conditions.
Recently the use of strong light-matter coupling has allowed for significant advancements in the manipulation of molecular properties.
The main goal of this thesis is providing a fundamental theoretical understanding of the effects induced by strong coupling on the spin and magnetic properties of molecules.
In the thesis new ab initio methodologies are developed to treat open-shell molecular systems in quantum electrodynamical environments. Direct interactions between the quantized field and the electronic spin are introduced, including external magnetic fields and relativistic corrections to the Hamiltonian.
A new configuration interaction based approach has been developed and efficiently implemented to investigate the magnetic properties of medium sized molecules strongly interacting with photons.
In the last part of the thesis interesting systems usually used for quantum computing applications have been investigated.
The developed methodology is also able to suggest new strategies for the implementation of qubits and quantum logical gates.
Finally future perspectives of the work will be presented and discussed.