  We report the electronic properties of the quadruple perovskite
CaCu$_{3}$Ti$_{4}$O$_{12}$ as obtained via several density-functional based
methods, and propose a new interpretation of optical experiments to the effect
that four distinct transitions (centered around 0.7, 1.5, 2.5, and 3.5 eV)
contribute to the spectrum. The comparison with experiment is satisfactory,
especially after we account for the effects of spin disorder, which does not
close the fundamental gap but suppresses the transition intensity. We find that
some of the methods we employ tend to overestimate considerably the gaps for
standard values of the respective adjustable parameters.
