  Materials with strong electronic Coulomb interactions play an increasing role
in modern materials applications. "Thermochromic" systems, which exhibit
thermally induced changes in their optical response, provide a particularly
interesting case. The optical switching associated with the metal-insulator
transition of vanadium dioxide (VO2), for example, has been proposed for use in
"intelligent" windows, which selectively filter radiative heat in hot weather
conditions. In this work, we develop the theoretical tools for describing such
a behavior. Using a novel scheme for the calculation of the optical
conductivity of correlated materials, we obtain quantitative agreement with
experiments for both phases of VO2. On the example of an optimized
energy-saving window setup, we further demonstrate that theoretical materials
design has now come into reach, even for the particularly challenging class of
correlated electron systems.
