Growth of Ni nanoclusters on irradiated graphene: a molecular dynamics study

Reactive molecular dynamics study on the thermal decomposition reaction of a triple-base solid propellant

The study of the combustion property of newly designed propellant by means of computational simulation is an efficient pathway for assessment and could avoid exposure to hazardous chemicals. An RDX-modified triple-base solid propellant formula was proposed in this study. Reactive molecular dynamics simulations employing ReaxFF-lg force field were performed to explore the thermal decomposition property of the propellant for a variety of temperatures. The reaction kinetics of the system and major ingredients were analyzed, and the apparent decomposition activation energies were calculated. The population of decomposition intermediates and products is thoroughly investigated. H₂O is consumed at high temperatures indicating a water-gas reaction that could reduce carbon clusters during the combustion of solid propellant. The water-gas reaction, as well as the population of H₂ at high temperature, points out the way of adjusting the formula of the propellant, which is adding fuel and oxidizer to improve combustion temperature and oxygen balance.

First-Principles Identification of Single Photon Emitters Based on Carbon Clusters in Hexagonal Boron Nitride

A recent study associates carbon with single photon emitters (SPEs) in hexagonal boron nitride (h-BN). This observation, together with the high mobility of carbon in h-BN, suggests the existence of SPEs based on carbon clusters. Here, by means of density functional theory calculations, we studied clusters of substitutional carbon atoms up to tetramers in h-BN. Two different conformations of neutral carbon trimers have zero-point line energies and shifts of the phonon sideband compatible with typical photoluminescence spectra. Moreover, some conformations of two small C clusters next to each other result in photoluminescence spectra similar to those found in the experiments. We also showed that vacancies are unable to reproduce the typical features of the phonon sideband observed in most measurements because of the large spectral weight of low-energy breathing modes, ubiquitous in such defects.

First-principles study of Ni adatom migration on graphene with vacancies

A theoretical study based on first-principles calculations about the interaction and diffusion of Ni atoms on pristine graphene and graphene with a single vacancy is presented. In the first case, we explored the structural changes due to the adsorption of Ni on graphene and the effects on the electronic structure. In the case of graphene with a vacancy, we analyzed the impact of the adsorbed Ni atom on the distortion of the graphene structure and how it depends on the distance from the graphene defect. In the analysis, we observed the changes in the electron localization function and the charge density. By knowing the interaction map of Ni with graphene, and the structural changes of the network, we performed energy barrier calculations within the climbing image nudged elastic band methodology to study the nickel diffusion. Finally, we explored how the vacancy and structural distortions affect the minimum energy paths and the saddle points for nickel moving away, around, and towards the vacancy.