Response theory constitutes a powerful and versatile theoretical framework for determining molecular properties and spectra by probing the response to weak (external or internal) electromagnetic fields. It provides efficient computational formulas for both linear and nonlinear response properties, thus describing a plethora of optical effects. Rooted on recent theoretical developments based within the coupled-cluster ansatz and density functional theory, in particular the so-called “damped” formulation of response theory, aka complex polarization propagator, we present results for both “traditional” and new “perspective” spectroscopies related to the absorption of light by the sample in presence external or internal magnetic fields, and in the highly energetic x-ray frequency region.
