Violet phosphorus is another promising layered semiconducting elemental structure for electronic and optoelectronic applications. Violet phosphorus quantum dots (VPQDs) have unique optical and electronic properties due to quantum mechanics. However,...

GaAs nanowires (NWs) often exhibit wurtzite crystal structure during the vapor−liquid−solid (VLS) growth, and their sidewalls are generally composed of {11̅ 00} and {112̅ 0} facets. Owing to the large surface-to-volume ratio, the sidewall structures of NWs are sensitive to the chemical environment. However, the impact of chemical environment on the sidewall structures and electronic properties of wurtzite GaAs NWs is still not clear. Here we present detailed first-principles calculations to investigate the atomic structure of sidewall facets, equilibrium crystal shape, and electronic properties of wurtzite GaAs NWs under different chemical potential conditions. On the basis of the surface energies of sidewall facets, the equilibrium crystal shape (ECS) of NWs is evaluated using the Wulff construction. The ECS of NWs demonstrates a shape evolution from a dodecagonal prism to a hexagonal prism with increasing As chemical potential, which is in agreement with the experimental observations. Meanwhile, the increasing As chemical potential results in a direct−indirect band gap transition in wurtzite GaAs NWs due to the structural change of NW sidewalls. This result can be applied successfully to explain an existing experimental controversy for the band gap of wurtzite GaAs NWs.

The controlled desilication of zeolites, leading to hierarchical micro-/mesoporous materials, is one of the most promising approaches to increase the application potential of zeolites. It can lift the restrictions connected to diffusion limitations in many industrially important processes and it can also modify the Si/Al ratio of the final material. The selective desilication of zeolites is generally performed under alkaline conditions, and control over the degree of framework degradation is maintained via the Si:Al ratio of the parent sample and the pH of the solution. However, the mechanism of alkaline hydrolysis in zeolites is poorly understood at present: the role of microsolvation of ions and the role of micropore confinement effects are currently unknown. In this work, we establish the mechanisms for the alkaline hydrolysis of siliceous zeolite chabazite (CHA) occurring from within the pore. Energetically facile reaction pathways are identified, which directly involve NaOH and confirm that NaOH may not only play a role as a reactant but also as a catalyst. We demonstrate that collective effects play a decisive role in the mechanism: initiation of the reaction via formation of Q3 defects becomes spontaneous when the Na+ cation is solvated by a sufficient amount of water and subsequent barriers along the desilication pathway are lowered. We show that it is crucial to include a realistic treatment of the hydration environment to capture the processes, which occur inside zeolite pores. This work advances our understanding of a ubiquitous process in heterogeneous catalysts and will help in controlled desilication treatments for zeolite upgrading.

On the basis of the recently reported X-ray crystal structure of light-harvesting complex 1-reaction center (LH1-RC) complex from Thermochromatium tepidum, we investigate electronic structures and pigment-protein interactions in the RC complex from a theoretical perspective. Hybrid quantum-mechanics/molecular-mechanics methods in combination with molecular dynamics simulations are employed to study environmental effects on excitation energies of RC cofactors with the consideration of a dynamic environment. The environmental effects are found to be essential for electronic structure determination. The special pair, a dimer of bacteriochlorophylls which serves as the primary electron donor in the bacterial RC, is our focus in this work. The first excited state of the special pair is found to have the lowest excitation energy of all molecules in the system, making it the most likely populated site after the excitation transfer. The transition charges from electrostatic potentials and the point dipole approximation have been applied to calculate the electronic coupling between individual pigments and that between the special pair and other pigments. Stronger electronic coupling is obtained between the P molecule and the L branch pigments than that between the P and the pigments in the M branch. Quantum chemical calculations reveal charge transfer characteristics of the first excited state of the special pair. It follows that charge separation takes place along the L branch in the RC. Spectral densities for all the cofactors are also calculated.

The Assembly–Disassembly–Organization–Reassembly (ADOR) process has been used extensively to prepare new zeolite frameworks based on germanosilicate precursors. The disassembly step exploits the lability of the bonds in the presence of water to selectively disconnect the framework, prior to reorganization into new framework topologies. However, a mechanistic understanding of this crucial step is lacking: specifically, the roles of heteroatom (germanium) content and water loading in zeolite hydrolytic instability. In this work, ab initio free energy simulations, coupled with water vapor adsorption measurements reveal that collectivity effects control the reactivity of the archetypal ADORable zeolite UTL toward water. A transition between reversible and irreversible water adsorption occurs as water loading is increased, leading to reactive transformations. Clustering of germanium is observed to activate hitherto unreported favorable hydrolysis mechanisms beyond a threshold concentration of three atoms per double four ring unit, demonstrating that the heteroatom distribution and collectivity in the hydrolysis mechanism can drastically influence zeolite framework instability. These findings suggest that control over heteroatom content, distribution, and hydration level is important to achieve the controlled partial hydrolysis of zeolitic frameworks and is likely to apply not only to other ADORable germanosilicate zeolites but also to Lewis acidic zeolites in general.