Double perturbation theory: A powerful tool in computational coordination chemistry

Quantum mechanical double perturbation theory offers a route to access a large variety of important chemical and physical molecular properties. The properties that are considered here can be defined as the second derivative of the total energy of a molecule with respect to perturbation parameters arising from, e.g. frequency-dependent or -independent external electric and magnetic fields, nuclear and electronic magnetic moments, relativistic corrections, nuclear displacements, etc. The accessible properties cover, among others, the important fields of electronic and vibrational spectra, nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and optical activity. We will outline the methodology that gives access to these properties, and discuss a number of them in detail together with applications to transition metal compounds. All these properties are treated within the same theoretical framework in order to illustrate the similarities between them.