We present an ab initio computational study of the Auger electron spectrum of benzene. Auger electron spectroscopy exploits the Auger-Meitner effect and, al- though it is established as an analytic technique, the theoretical modeling of molecular Auger spectra from first principles remains challenging. Here, we use coupled- cluster and equation-of-motion coupled-cluster theory combined with two approaches to describe the decaying nature of core-ionized states: (i) Feshbach-Fano resonance theory and (ii) the method of complex basis functions. The spectra computed with these two approaches are in excellent agreement with each other and also agree well with experimental Auger spectra of benzene. The Auger spectrum of benzene features two well-resolved peaks at Auger electron energies above 260 eV that cor- respond to final states with two electrons removed from the 1e1g and 3e2g highest occupied molecular orbitals. At lower Auger electron energies, the spectrum is less well resolved and the peaks comprise multiple final states of the benzene dication. In line with theoretical considerations, singlet decay channels contribute more to the total Auger intensity than the corresponding triplet decay channels.

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The aim of this work is to describe the molecular inclusion of chlordecone with α-, β-, and γ-cyclodextrin in aqueous solution using quantum mechanics. The guest–host complexes of chlordecone and cyclodextrins are modeled in aqueous solution using the multiple minima hypersurface methodology with a PM6-D3H4X semiempirical Hamiltonian, and the lowest energy minima obtained are reoptimized using the M06-2X density functional and the intermolecular interactions described using quantum theory of atoms in molecules (QTAIM). The studied complexes are classified according to the degree of inclusion, namely, total occlusion, partial occlusion, and external interaction. More stable complexes are obtained when γ-CD is used as the host molecule. The interactions characterized through QTAIM analysis are all of electrostatic nature, predominantly of dispersive type. In this work, a method based on the counterpoise correction is also discussed to mitigate the basis set superposition error in density functional theory calculations when using an implicit solvation model.

Explaining the interactions between metaldehyde and acidic surface groups of activated carbon under different pH conditions.

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