Effective hadron models commonly require the computation of functional
determinants. In the static case these are one--loop vacuum polarization
energies, known as Casimir energies. In this talk I will present general
methods to efficiently compute renormalized one--loop vacuum polarization
energies and energy densities and apply these methods to construct soliton
solutions within a variational approach. This calculational method is
particularly useful to study singular limits that emerge in the discussion of
the {\it classical} Casimir problem which is usually posed as the response of a
fluctuating quantum field to externally imposed boundary conditions.Comment: 14 pages, LaTeX. Talk presented at the at the second intl. workshop
``Effective Theories of Low Energy QCD'', Coimbra, Sept. 200
