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In the low-frequency regime, ≈1 THz, glasses show an anomalous excess in their vibrational density of states called the boson peak (BP). The origin of BP has been a subject of debate since its first discovery a few decades ago. Although BP has been the focus of numerous studies, no conclusive answers have been found about its origins, which remained elusive to date. Here, we present results based on molecular dynamics of several binary and ternary silicate glasses with different network intermediates and modifier oxides. The vibrational density of states and the BP are reported for all the studied glasses. Their correlation with the elastic constant C 44 , structural, and dynamical properties are extensively discussed in terms of Voronoi atomic volume and the vibrational mean square displacement of Q 4 species specifically. We also question the classical classification of alkali oxides as modifiers, and we suggest that Li 2 O plays the role of pseudo-intermediate oxide in lithium silicate glasses. This claim is supported by the effect of Li on various vibrational modes, and this effect differs from the other alkali metals. Furthermore, we demonstrate a correlation between the BP intensities and both the Voronoi volume of the Q 4 and Q 3 units and vibrational mean square displacements.

We conducted an extensive investigation using density functional theory (DFT) calculations and ReaxFF molecular dynamics (MD) simulations to elucidate the mechanisms of desulfurization and denitrogenation on Cu(100) surfaces. This study encompassed both pristine surfaces and those modified with Pt or Rh transition metals. Our primary objective was to gain a deep understanding of the adsorption behavior of thiophene (C 4 H 4 S) and pyridine (C 5 H 5 N) molecules on stepped Cu(100) surfaces, which serve as models for sulfur and nitrogen compounds. We systematically explored the interplay among water, adsorption efficiency, and surface regeneration capabilities. Using DFT, we thoroughly examined various aspects, including interaction energies, charge transfers, changes in electron density, and alterations in work function upon molecule adsorption. Notably, we observed a decrease in the interaction energy of thiophene, whereas that of pyridine increased when adsorbed on Pt/Rh-doped surfaces compared to pristine ones. Thiophene adsorption reduced the work function, potentially enhancing detectability, without causing inhibitory effects on any surface. Stepped Cu(100) surfaces demonstrated a strong affinity for thiophene, exhibiting an energy difference of approximately 86 kJ mol -1 . However, this trend reversed on doped surfaces, where pyridine displayed stronger adsorption than thiophene, resulting in energy differences of around 123 kJ mol -1 and 62 kJ mol -1 on Pt-Cu and Rh-Cu surfaces, respectively. Moreover, our investigation highlighted the regeneration capacity of these surfaces, indicating that all surfaces can be considered promising candidates for desulfurization, while only Cu and Pt-Cu surfaces were found to be suitable for denitrogenation. Furthermore, results from MD simulations in combination with potential of mean force (PMF) simulations at 300 K, aligned with DFT calculations, confirmed the adsorption configurations of pyridine and thiophene. This analysis demonstrated the competitive advantage of thiophene over pyridine in adsorption and highlighted the inhibitory effect of water on pyridine adsorption on the Cu(100) surface.

The paper elucidates the main driving mechanisms at play during the early stage of the Ti/CuO thermite reaction using reactive forcefields in the frame of molecular dynamics calculations. Results show that TiO preferentially forms in immediate contact to pure Ti at temperatures as low as 200 K rather than TiO 2 . Increasing the temperature to 700 K, the 2 nm TiO 2 in contact to Ti is found to be homogeneously depleted from half of its oxygen atoms. Also, the first signs of CuO decomposition are observed at 600 K, in correlation with the impoverishment in oxygen atom reaching the titanium oxide layer immediately in contact to CuO. Further quantification of the oxygen and titanium mass transport at temperatures above 700 K suggests that mostly oxygen atoms migrate from and across the titanium oxide interfacial layer to further react with the metallic titanium fuel reservoir. This scenario is opposed to the one of the Al/CuO system, for which the mass transport is dominated by the Al fuel diffusion across alumina. Further comparison of both thermites sheds light on the enhanced reactivity of the Ti-based thermite, for which CuO decomposition is promoted at lower temperature, and offers a novel understanding of thermite initiation at large.

This theoretical work aims to understand the influence of nanopores at CuO-Al nanothermite interfaces on the initial stage of thermite reaction. ReaxFF molecular dynamics simulations were run to investigate the chemical and structural evolution of the reacting interface between the fuel, Al, and oxidizer, CuO, between 400 and 900 K and considering interfaces with and without a pore. Results show that the initial alumina layer becomes enriched with Al and grows primarily into the Al metal at higher temperatures. The modification of alumina is driven by simultaneous Al and O migration between metallic Al and the native amorphous Al 2 O 3 layer. However, the presence of a pore significantly affects the growth kinetics and the composition of this alumina layer at temperatures exceeding 600 K, which impacts the initiation properties of the nanothermite. In the system without a pore, where Al is in direct contact with CuO, a ternary aluminate layer, a mixture of Al, O, and Cu, is formed at 800 K, which slows Al and O diffusion, thus compromising the nanothermite reactivity in fully dense Al/CuO composites. Conversely, the presence of a pore between Al and CuO promotes Al enrichment of the alumina layer above 600 K. At that temperature, any free oxygen molecules in the pore become attached to the reactive alumina surface resulting in a rapid oxygen pressure drop in the pore. This is expected to accelerate the reduction of the adjacent CuO as observed in experiments with Al/CuO composites with porosity at the CuO-Al interfaces.

We study reactivity and leaching at the calcium sodium borosilicate (CNBS)-water interface by means of a Car-Parrinello ab initio molecular dynamics simulation over a simulation time of 100 ps. With an emphasis on the comparison between the behaviors of Ca 2+ and Na + cations at the CNBS glass-water interface, different mechanism events during the trajectory are revealed, discussed, and correlated with other density functional theory calculations. We show that Na + ions can be released in solution, while Ca 2+ cannot leave the surface of CNBS glass. This release is correlated with the vacancy energy of Ca 2+ and Na + cations. Here, we found that the CNBS structure with the Na + cation vacancy is energetically more favorable than the structure with the Ca 2+ cation vacancy. The calcium adsorption site has been shown to have a greater affinity for water than can be found in the case of the sodium site, demonstrating that affinity may not be considered a major factor controlling the release of cations from the glass to the solution.

Graphene oxide (GO) represents a complex family of materials related to graphene: easy to produce in large quantities, easy to process, and convenient to use as a basis for further functionalization, with the potential for wide-ranging applications such as in nanocomposites, electronic inks, biosensors and more. Despite their importance, the key structural traits of GO, and the impact of these traits on properties, are still poorly understood due to the inherently berthollide character of GO which complicates the establishment of clear structure/property relationships. Widely accepted structural models of GO frequently neglect the presence of extended topological defects, structural changes to the graphene basal plane that are not removed by reduction methods. Here, a combination of experimental approaches and molecular simulations demonstrate that extended topological defects are a common feature across GO and that the presence of these defects strongly influences the properties of GO. We show that these extended topological defects are produced following even controlled 'gentle' functionalization by atomic oxygen and are comparable to those obtained by a conventional modified Hummers' method. The presence of the extended topological defects is shown to play an important role in the retention of oxygen functional groups after reduction. As an exemplar of their effect on the physical properties, we show that the GO sheets display a dramatic decrease in strength and stiffness relative to graphene and, due to the presence of extended structural defects, no improvement is seen in the mechanical properties after reduction. These findings indicate the importance of extended topological defects to the structure and properties of functionalized graphene, which merits their inclusion as a key trait in simple structural models of GO.