We
report in the present paper a comprehensive investigation of
representative Pt(II) and Ir(III) complexes with special reference
to their one-photon absorption spectra employing methods rooted in
density functional theory and its time dependent extension. We have
compared nine different functionals ranging from generalized gradient
approximation (GGA) to global or range-separated hybrids, and two
different basis sets, including pseudopotentials for 4 iridium and
7 platinum complexes. It turns out that hybrid functionals with the
same exchange part give comparable results irrespective of the specific
correlation functional (i.e., B3LYP is very close to B3PW91 and PBE0
is very close to MPW1PW91). More recent functionals, such as CAM-B3LYP
and M06-2X, overestimate excitation energies, whereas local functionals
(BP86 -GGA-, M06-L -Meta GGA-) strongly underestimate transition energies
with respect to experimental results. As expected, basis set effects
are weak, and the use of a triple-ζ polarized (def2-TZVP) basis
set does not significantly improve the computed excitation energies
with respect to a classical double-ζ basis set (LANL2DZ) augmented
by polarization functions, but it significantly raises the computational
effort