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.