  We formulate the Hartree-Fock method using a functional integral approach.
Then we consider a nonperturbative component of the vacuum polarization. For
the Dirac-Coulomb operator the renormalization flow of the vacuum polarization
is calculated numerically. For the Hartree-Fock operator the polarization is
obtained by integrating an appropriately rescaled flow. The text includes an
approximate calculation of the vacuum polarization in Uranium.
