Mixedab initioquantum mechanical and Monte Carlo calculations of secondary emission fromSiO2nanoclusters

Abstract

A mixed quantum mechanical and Monte Carlo method for calculating Auger spectra from nanoclusters is presented. The approach, based on a cluster method, consists of two steps. Ab initio quantum mechanical calculations are first performed to obtain accurate energy and probability distributions of the generated Auger electrons. In a second step, using the calculated line shape as electron source, the Monte Carlo method is used to simulate the effect of inelastic losses on the original Auger line shape. The resulting spectrum can be directly compared to "as-acquired" experimental spectra, thus avoiding background subtraction or deconvolution procedures. As a case study, the O K-LL spectrum from solid SiO 2 is considered. Spectra computed before or after the electron has traveled through the solid, i.e., unaffected or affected by extrinsic energy losses, are compared to the pertinent experimental spectra measured within our group. Both transition energies and relative intensities are well reproduced.

Electron spectroscopies and inelastic processes in nanoclusters and solids: Theory and experiment

“…A large number of ab initio calculations have been performed to predict the Auger energies of atomic and molecular spectra and the results obtained are generally in fairly good agreement with the experimental data; see, e.g., [42,49,[132][133][134][135][136][137][138][139][140][141][142]. Very different is the situation for solids and extended systems, where the theoretical and computational treatment of electronic excitations, particularly neutral ones, still presents many difficulties.…”

“…In a second step, ab initio quantum mechanical calculations, without free parameters, are performed to obtain accurate energy transitions and probability distributions. In a third step, using the calculated lineshape as the electron source, the effect of extrinsic energy losses on the original lineshape is simulated [27,133] by the Monte Carlo method [105,223]. This is a completely new feature in the landscape of ab initio electron spectroscopy calculations, allowing one to compare directly the computed spectrum to measured spectra, avoiding background subtraction [224,225], a procedure not free from uncertainty.…”

A Bird’s Eye View on the Concept of Multichannel Scattering with Applications to Materials Science, Condensed Matter, and Nuclear Astrophysics

“…At variance, the goal of this opinion article is to provide a "bird's eye view" on a recently developed ab initio method (Taioli et al, 2009b(Taioli et al, ,c, 2010, firstly implemented to perform spectral analysis of solids at drastically reduced computational cost. This method has been further extended, as well as successfully used, in apparently distant applications, ranging from materials science to astrophysics.…”

“…Hereby, after a description of the conceptual framework behind this approach we will prove its ability to span different research fields by interpreting a specific set of physical problems in the meV to MeV range. In particular, we will discuss the Auger effect in SiO 2 (Taioli et al, 2009b), the BEC-BCS crossover in ultracold Fermi gases (UFG) (Simonucci et al, 2011(Simonucci et al, , 2012Garberoglio et al, 2013), and finally the electron capture in stellar plasma .…”

“…To take into account both extrinsic and intrinsic features on the same grounds, we proposed a unified method able to calculate electron spectra in solids (Taioli et al, 2009b(Taioli et al, ,c, 2010) using beyond meanfield techniques. This method provides an extension of Fano's resonant multichannel scattering, allowing several intermediate quasi bound states (see Eq.…”