Statistics-Based Analysis of the Evolution of Structural and Electronic Properties of Realistic Amorphous Alumina During the Densification Process: Insights from First-Principles Approach

On the basis of the melt and quench strategy, over 3000 structurally different AlO_<i>x</i> structures have been generated using <i>ab initio</i> molecular dynamics. Unlike other previous studies where defects were introduced into some crystalline polymorph of Al₂O₃, a variety of defects emerged directly from this approach. A new way to probe the short (distances between first neighbors and coordination numbers) and medium (atom rings, bond angles, and distances between second neighbors) range structural properties of H- and/or O-rich AlO_<i>x</i> has been defined. The evolution of such structural properties during the densification process with mass loss has been studied using averaged data at a fixed chemical composition. A good agreement is observed between experimental and theoretical structural data, validating the methodology. In particular, the profile of the total experimental neutron pair correlation function has been rationalized. At fixed composition, the Spearman correlations have been calculated in order to reveal monotonic relationships between properties: a correlation between the structure and band gap energy of different stoichiometries of AlO_<i>x</i> could not be clearly inferred. Finally, we may speculate that the O₂^2– and Al–H defects could explain the origin of negative fixed charges in AlO_<i>x</i> because of their effects on electronic properties of AlO_<i>x</i> and their structural characteristics

Decoupling the Effects of Mass Density and Hydrogen‑, Oxygen‑, and Aluminum-Based Defects on Optoelectronic Properties of Realistic Amorphous Alumina

The search for functional materials is currently hindered by the difficulty to find significant correlation between constitutive properties of a material and its functional properties. In the case of amorphous materials, the diversity of local structures, chemical composition, impurities and mass densities makes such a connection difficult to be addressed. In this Letter, the relation between refractive index and composition has been investigated for amorphous AlO_<i>x</i> materials, including nonstoichiometric AlO_<i>x</i>, emphasizing the role of structural defects and the absence of effect of the band gap variation. It is found that the Newton–Drude (ND) relation predicts the refractive index from mass density with a rather high level of precision apart from some structures displaying structural defects. Our results show especially that O- and Al-based defects act as additive local disturbance in the vicinity of band gap, allowing us to decouple the mass density effects from defect effects (<i>n</i> = <i>n</i>[ND] + Δ<i>n</i>_defect)

Benchmarking DFT and TD-DFT Functionals for the Ground and Excited States of Hydrogen-Rich Peptide Radicals

We assess the pros and cons of a large panel of DFT exchange-correlation functionals for the prediction of the electronic structure of hydrogen-rich peptide radicals formed after electron attachment on a protonated peptide. Indeed, despite its importance in the understanding of the chemical changes associated with the reduction step, the question of the attachment site of an electron and, more generally, of the reduced species formed in the gas phase through electron-induced dissociation (ExD) processes in mass spectrometry is still a matter of debate. For hydrogen-rich peptide radicals in which several positive groups and low-lying π* orbitals can capture the incoming electron in ExD, inclusion of full Hartree–Fock exchange at long-range interelectronic distance is a prerequisite for an accurate description of the electronic states, thereby excluding several popular exchange-correlation functionals, e.g., B3LYP, M06-2X, or CAM-B3LYP. However, we show that this condition is not sufficient by comparing the results obtained with asymptotically correct range-separated hybrids (M11, LC-BLYP, LC-BPW91, ωB97, ωB97X, and ωB97X-D) and with reference CASSCF-MRCI and EOM-CCSD calculations. The attenuation parameter ω significantly tunes the spin density distribution and the excited states vertical energies. The investigated model structures, ranging from methylammonium to hexapeptide, allow us to obtain a description of the nature and energy of the electronic states, depending on (i) the presence of hydrogen bond(s) around the cationic site(s), (ii) the presence of π* molecular orbitals (MOs), and (iii) the selected DFT approach. It turns out that, in the present framework, LC-BLYP and ωB97 yields the most accurate results

Binding of Thioflavin T and Related Probes to Polymorphic Models of Amyloid‑β Fibrils

Alzheimer’s disease is a challenge of the utmost importance for contemporary society. An early diagnosis is essential for the development of treatments and for establishing a network of support for the patient. In this light, the deposition in the brain of amyloid-β fibrillar aggregates, which is a distinctive feature of Alzheimer, is key for an early detection of this disease. In this work we propose an atomistic study of the interaction of amyloid tracers with recently published polymorphic models of amyloid-β 1–40 and 1–42 fibrils, highlighting the relationship between marker architectures and binding affinity. This work uncovers the importance of quaternary structure, and in particular of junctions between amyloid-β protofilaments, as the key areas for marker binding