Recently synthesized two-dimensional (2D) boron, borophene, exhibits a novel metallic behavior rooted in the s–p orbital hybridization, distinctively different from other 2D materials such as sulfides/selenides and semi-metallic graphene. This unique feature of borophene implies new routes for charge delocalization and band gap opening. Herein, using first-principles calculations, we explore the routes to localize the carriers and open the band gap of borophene via chemical functionalization, ribbon construction, and defect engineering. The metallicity of borophene is found to be remarkably robust against H- and F-functionalization and the presence of vacancies. Interestingly, a strong odd–even oscillation of the electronic structure with width is revealed for H-functionalized borophene nanoribbons, while an ultra-high work function (∼7.83 eV) is found for the F-functionalized borophene due to its strong charge transfer to the atomic adsorbates.

Reactive magnesium oxide (MgO)-based cement (RMC) can play a key role in carbon capture processes. However, knowledge on the driving forces that control the degree of carbonation and hydration and rate of reactions in this system remains limited. In this work, density functional theory-based simulations are used to investigate the physical nature of the reactions taking place during the fabrication of RMCs under ambient conditions. Parametric indicators such as adsorption energies, charge transfer, electron localization function, adsorption/dissociation energy barriers, and the mechanisms of interaction of H₂O and CO₂ molecules with MgO and brucite (Mg(OH)₂) clusters are considered. The following hydration and carbonation interactions relevant to RMCs are evaluated: (i) carbonation of MgO, (ii) hydration of MgO, carbonation of hydrated MgO, (iii) carbonation of Mg(OH)₂, (iv) hydration of Mg(OH)₂, and (v) hydration of carbonated Mg(OH)₂. A comparison of the energy barriers and reaction pathways of these mechanisms shows that the carbonation of MgO is hindered by the presence of H₂O molecules, while the carbonation of Mg(OH)₂ is hindered by the formation of initial carbonate and hydrate layers as well as presence of excessed H₂O molecules. To compare these finding to bulk mineral surfaces, the interactions of the CO₂ and H₂O molecules with the MgO(001) and Mg(OH)₂ (001) surfaces are studied. Therefore, this work presents deep insights into the physical nature of the reactions and the mechanisms involved in hydrated magnesium carbonates production that can be beneficial for its development.

Antimonene, a new group-VA 2D semiconducting material beyond phosphorene, has been recently synthesized through various approaches and shown to exhibit good structural integrity under ambient conditions and various interesting properties. In this study, we performed systematical first-principles investigations on the interactions of antimonene with the small molecules CO, NO, NO₂, H₂O, O₂, NH₃, and H₂. It was found that NO, NO₂, H₂O, O₂, and NH₃ served as charge acceptors, whereas CO showed a negligible charge transfer. H₂ acted as a charge donor to antimonene, and the amount of charge transfer was ten times that of H₂ on phosphorene. The interaction of the O₂ molecule with antimonene is much stronger than that with phosphorene. Surprisingly, the kinetic barrier for the splitting of O₂ molecule on antimonene is low (∼0.40 eV), suggesting that pristine antimonene may undergo oxidation under ambient conditions, especially at elevated temperatures. Fortunately, the acceptor role of H₂O on antimonene, contrary to its donor role on phosphorene, helps to suppress further structural degradation of the oxidized antimonene by preventing proton transfer between water molecules and oxygen species to form acids. Upon comparing antimonene with phosphorene and InSe, we suspected that the acceptor role of water may be a necessary condition for good environmental stability of these 2D layers to avoid structural decomposition. Although the surface oxidation layer may serve as an effective passivation layer, preventing further degradation of the underlying layers, our findings show that the antimonene layers still need to be separated or properly protected by other noncovalent functionalization from oxygen or other environmental molecules. The present study reveals interesting insights into the environmental effects of physisorbed small molecules on the oxidation tendency and stability of antimonene that may be important for its growth, storage, and applications.

Layered indium selenide (InSe), a new two-dimensional (2D) material with a hexagonal structure and semiconducting characteristics, is gaining increasing attention owing to its intriguing electronic properties. Here, by using first-principles calculations, we reveal that perfect InSe possesses high chemical stability against oxidation, superior to MoS₂. However, the presence of intrinsic Se vacancy (V_Se) and light illumination can markedly affect its surface activity. In particular, the excess electrons associated with the exposed In atoms at the V_Se site under illumination are able to remarkably reduce the dissociation barrier of O₂ to ∼0.2 eV. Moreover, under ambient conditions, the splitting of O₂ enables the formation of substitutional (apical) oxygen atomic species, which further cause the trapping and subsequent rapid splitting of H₂O molecules and ultimately the formation of hydroxyl groups. Our findings uncover the causes and underlying mechanisms of InSe surface degradation via defect-photo-promoted oxidations. Such results will be beneficial in developing strategies for the storage of the InSe material and its applications for surface passivation with boron nitride, graphene or In-based oxide layers.

Structural stability of bismuthene may originate from an acceptor role of water molecules on it.

An ansatz has been proposed for setting the initial conditions in the molecular dynamics study of moving discrete breathers in monoatomic close packed crystals. The applicability of the ansatz has...