  We present ultra-fast quantum chemical methods for the calculation of
infrared and ultraviolet-visible spectra designed to provide fingerprint
information during autonomous and interactive explorations of molecular
structures. Characteristic spectral signals can serve as diagnostic probes for
the identification and characterization of molecular structures. These features
often do not require ultimate accuracy with respect to peak position and
intensity, which alleviates the accuracy-time dilemma in ultra-fast electronic
structure methods. If approximate ultra-fast algorithms are supplemented with
an uncertainty quantification scheme for the detection of potentially large
prediction errors in signal position and intensity, an offline refinement will
always be possible to confirm or discard the predictions of the ultra-fast
approach. Here, we present ultra-fast electronic structure methods for such a
protocol in order to obtain ground- and excited-state electronic energies,
dipole moments, and their derivatives for real-time applications in vibrational
spectroscopy and photophysics. As part of this endeavor, we devise an
information-inheritance partial Hessian approach for vibrational spectroscopy,
a tailored subspace diagonalization approach and a determinant-selection scheme
for excited-state calculations.
