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Why does silicon have an indirect band gap?
Mater Horiz
January 2025
Department of Materials Science, University of Michigan, Ann Arbor, Michigan 48109, USA.
It is difficult to intuit how electronic structure features-such as band gap magnitude, location of band extrema, effective masses, -arise from the underlying crystal chemistry of a material. Here we present a strategy to distill sparse and chemically-interpretable tight-binding models from density functional theory calculations, enabling us to interpret how multiple orbital interactions in a 3D crystal conspire to shape the overall band structure. Applying this process to silicon, we show that its indirect gap arises from a competition between first and second nearest-neighbor bonds-where second nearest-neighbor interactions pull the conduction band down from Γ to X in a cosine shape, but the first nearest-neighbor bonds push the band up near X, resulting in the characteristic dip of the silicon conduction band.
View Article and Find Full Text PDFUnderstanding the synergistic interaction between a 1,3,4-thiadiazole derivative and amphotericin B using spectroscopic and theoretical studies.
Sci Rep
December 2024
Department of Biophysics, Faculty of Environmental Biology, University of Life Sciences in Lublin, Akademicka 13, 20-950, Lublin, Poland.
We present a comprehensive spectroscopic study supported by theoretical quantum chemical calculations conducted on a molecular system (4-(5-methyl-1,3,4-thiadiazol-2-yl)benzene-1,3-diol (C1) and the antibiotic Amphotericin B (AmB)) that exhibits highly synergistic properties. We previously reported the strong synergism of this molecular system and now wish to present related stationary measurements of UV-Vis absorption, fluorescence, and fluorescence anisotropy in a polar, aprotic solvent (DMSO and a PBS buffer), followed by time-resolved fluorescence intensity and anisotropy decay studies using different ratios of the selected 1,3,4-thiadiazole derivative to Amphotericin B. Absorption spectra measured for the system revealed discrepancies in terms of the shapes of absorption bands, particularly in PBS.
View Article and Find Full Text PDFNon-adiabatic Couplings in Surface Hopping with Tight Binding Density Functional Theory: The Case of Molecular Motors.
J Chem Theory Comput
December 2024
Condensed Matter and Statistical Physics, The Abdus Salam International Centre for Theoretical Physics, 34151 Trieste, Italy.
Nonadiabatic molecular dynamics (NAMD) has become an essential computational technique for studying the photophysical relaxation of molecular systems after light absorption. These phenomena require approximations that go beyond the Born-Oppenheimer approximation, and the accuracy of the results heavily depends on the electronic structure theory employed. Sophisticated electronic methods, however, make these techniques computationally expensive, even for medium size systems.
View Article and Find Full Text PDFQuantum Simulations of Radiation Damage in a Molecular Polyethylene Analog.
Macromol Rapid Commun
December 2024
Department of Chemical Engineering, University of California Davis, One Shields Avenue, Davis, CA, 95616, USA.
An atomic-level understanding of radiation-induced damage in simple polymers like polyethylene is essential for determining how these chemical changes can alter the physical and mechanical properties of important technological materials such as plastics. Ensembles of quantum simulations of radiation damage in a polyethylene analog are performed using the Density Functional Tight Binding method to help bind its radiolysis and subsequent degradation as a function of radiation dose. Chemical degradation products are categorized with a graph theory approach, and occurrence rates of unsaturated carbon bond formation, crosslinking, cycle formation, chain scission reactions, and out-gassing products are computed.
View Article and Find Full Text PDFOrigin of unique electronic structures of single-atom alloys unraveled by interpretable deep learning.
J Chem Phys
October 2024
Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
We uncover the origin of unique electronic structures of single-atom alloys (SAAs) by interpretable deep learning. The approach integrates tight-binding moment theory with graph neural networks to accurately describe the local electronic structure of transition and noble metal sites upon perturbation. We emphasize the complex interplay of interatomic orbital coupling and on-site orbital resonance, which shapes the d-band characteristics of an active site, shedding light on the origin of free-atom-like d-states that are often observed in SAAs involving d10 metal hosts.
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