We present a detailed comparison of the S0, S1 (n -> \pi*) and S2 (\pi ->
\pi*) potential energy surfaces (PESs) of the prototypical molecular switch
azobenzene as obtained by Delta-self-consistent-field (Delta-SCF)
Density-Functional Theory (DFT), time-dependent DFT (TD-DFT) and approximate
Coupled Cluster Singles and Doubles (RI-CC2). All three methods unanimously
agree in terms of the PES topologies, which are furthermore fully consistent
with existing experimental data concerning the photo-isomerization mechanism.
In particular, sum-method corrected Delta-SCF and TD-DFT yield very similar
results for S1 and S2, when based on the same ground-state exchange-correlation
(xc) functional. While these techniques yield the correct PES topology already
on the level of semi-local xc functionals, reliable absolute excitation
energies as compared to RI-CC2 or experiment require an xc treatment on the
level of long-range corrected hybrids. Nevertheless, particularly the
robustness of Delta-SCF with respect to state crossings as well as its
numerical efficiency suggest this approach as a promising route to dynamical
studies of larger azobenzene-containing systems.Comment: 25 pages, 6 figure
