We investigate the basic quantum-mechanical processes behind the nonproportional response of scintillators to incident radiation responsible for reduced resolution. For this purpose, we conduct a comparative first-principles study of quasiparticle spectra on the basis of the G0W0 approximation as well as absorption spectra and excitonic properties by solving the Bethe-Salpeter equation for two ...

Pierluigi Cudazzo,1 Matteo Gatti,1 and Angel Rubio1,2 1Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Departamento Fı́sica de Materiales, Universidad del Paı́s Vasco UPV/EHU, Centro de Fı́sica de Materiales CSIC-UPV/EHU-MPC and DIPC, Avenida Tolosa 72, E-20018 San Sebastián, Spain 2Fritz-Haber-Institut der Max-Planck-Gesellschaft, Theory Department, Faradayweg 4-6, D-14195 Ber...

Collective spin excitations in magnetic materials arise from the correlated motion of electron-hole pairs with opposite spins. The pair propagation is described by the transverse magnetic susceptibility, which we calculate within many-body perturbation theory from first principles employing the full-potential linearized augmentedplane-wave formalism. Ferromagnetic materials exhibit a spontaneou...

We propose an alternative formulation of many-body perturbation theory that uses the density-functional concept. Instead of the usual four-point integral equation for the polarizability, we obtain a two-point one, which leads to excellent optical absorption and energy-loss spectra. The corresponding three-point vertex function and self-energy are then simply calculated via an integration, for a...

Relativistic third-order MBPT is applied to obtain energies of ions with two valence electrons in the no virtual-pair approximation (NVPA). A total of 302 third-order Goldstone diagrams are organized into 12 one-body and 23 two-body terms. Only third-order two-body terms and diagrams are presented here, owing to the fact that the one-body terms are identical to the previously studied third-orde...

An algorithm, based on numerical description of the terms of many-body perturbation theory (Goldstone diagrams), is presented. The algorithm assumes a basis set of orthogonal single-electron orbitals supplied by the user. These orbitals are the eigenstates of the Dirac operator in the spherically-symmetric case. Apart from this the algorithm is practically free from any limitations and can be u...

Theoretically the Kohn-Sham band gap differs from the exact quasiparticle energy gap by the derivative discontinuity of the exchange-correlation functional. In practice for semiconductors and insulators the band gap calculated within any local or semilocal density approximations underestimates severely the experimental energy gap. On the other hand, calculations with an "exact" exchange potenti...