  In this thesis, we focus on the energetic analysis within autonomous quantum
systems. To this aim, we propose a novel and general formalism for a dynamic
description of the energy exchanges between interacting subsystems. From the
Schmidt decomposition approach, we identify effective Hamiltonians as the
representative operators for characterizing the local internal energies, whose
expectation values satisfy the usual thermodynamic notion of energy additivity.
In contrast to the currently used methodologies, such procedure treats the
subsystems with equal footing and do not rely on any sort of approximations and
additional hypotheses, e.g., semi-classical description, weak-coupling regime,
strict energy conservation and Markovian dynamics. In short, our proposal
contributes to the development of QT by providing a new formalism that does not
suffer from the usual restrictive shortcomings and establishes a new and exact
route for defining other general thermodynamic quantities to the quantum
regime.
