  In this article it will be introduced a new theorem, can be considered a
generalization of Hellmann-Feynman theorem[1]. The latter used in conjunction
with the quantization of the free energy[2] of a quantum system allows to
derive strightly the electronic Heat variations of a quantum electronic system,
in its condensed phase of eigenstates, showing its agreement with classical
thermodynamics, making then possible to desing ab inito quantum models of the
electronic structure in its thermodynamical states.
