The many-body-theoretical basis and applications of theoretical spectroscopy of condensed
matter e.g. crystals nanosystems and molecules are unified in one advanced text for readers
from graduate students to active researchers in the field. The theory is developed from first
principles including fully the electron-electron interaction and spin interactions. It is based
on the many-body perturbation theory a quantum-field-theoretical description and Green's
functions. The important expressions for ground states as well as electronic single-particle
and pair excitations are explained. Based on single-particle and two-particle Green's functions
the Dyson and Bethe-Salpeter equations are derived. They are applied to calculate spectral and
response functions. Important spectra are those which can be measured using photoemission
inverse photoemission optical spectroscopy and electron energy loss inelastic X-ray
spectroscopy. Important approximations are derived and discussed in the light of selected
computational and experimental results. Some numerical implementations available in well-known
computer codes are critically discussed. The book is divided into four parts: (i) In the first
part the many-electron systems are described in the framework of the quantum-field theory. The
electron spin and the spin-orbit interaction are taken into account. Sum rules are derived.
(ii) The second part is mainly related to the ground state of electronic systems. The total
energy is treated within the density functional theory. The most important approximations for
exchange and correlation are delighted. (iii) The third part is essentially devoted to the
description of charged electronic excitations such as electrons and holes. Central
approximations as Hedin's GW and the T-matrix approximation are discussed.(iv) The fourth part
is focused on response functions measured in optical and loss spectroscopies and neutral pair
or collective excitations.
