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Pentazole (HN5) and its anion ( cyclo-N5-) have been elusive for nearly a century because of the unstable N5 ring. Recently, Zhang et al. reported the first synthesis and characterization of the pentazolate anion cyclo-N5- in (N5)6(H3O)3(NH4)4Cl salt at ambient conditions ( Science 2017, 355, 374 ). However, whether the cyclo-N5- in (N5)6(H3O)3(NH4)4Cl salt is protonated or not has been debated ( Huang and Xu, Science, 2018, 359, eaao3672 ; Jiang et al. Science, 2018, 359, aas8953 ). Herein, we employed ab initio molecular dynamics (AIMD) simulations, which can well present the dynamic behavior at realistic experimental conditions, to examine the potential protonated state of cyclo-N5- in both crystal and dimethyl sulfoxide (DMSO) solvent. Our simulations revealed that the protonation reaction of (N5)6(H3O)3(NH4)4Cl → (N5)5(N5H)(H2O)(H3O)2(NH4)4Cl is thermodynamically spontaneous according to Δ G < 0, and the small energy barrier of 12.6 kJ/mol is not enough to prevent the partial protonation of cyclo-N5- due to the temperature effect; consequently, both deprotonated and protonated cyclo-N5- exist in the crystal. In comparison, the DMSO solvent effect can remarkably reduce the difference of proton affinities among cyclo-N5-, H2O, and NH3, and the temperature effect can finally break these hydrogen bonds and lead to the deprotonated cyclo-N5- in DMSO solvent. Our AIMD simulations reconcile the recent controversy.

Pentazole (HN

van der Waals (vdW) epitaxy of ultrathin organic films on two-dimensional (2D) atomic crystals has become a sovereign area because of their unique advantages in organic electronic devices. However, the dynamic mechanism of the self-assembly remains elusive. Here, we visualize the nanoscale self-assembly of organic molecules on graphene and boron nitride monolayer from a disordered state to a 2D lattice via molecular dynamics simulation for the first time. It is revealed that the assembly toward 2D ordered structures is essentially the minimization of the molecule-molecule interaction, that is, the vdW interaction in nonpolar systems and the vdW and Coulomb interactions in polar systems that are the decisive factors for the formation of the 2D ordering. The role of the substrate is mainly governing the array orientation of the adsorbates. The mechanisms unveiled here are generally applicable to a broad class of organic thin films via vdW epitaxy.

Ultrathin indium selenide (InSe), as a newly emerging two-dimensional material with high carrier mobility and a broad absorption spectrum, has been the focus of current research. However, the long-term environmental instability of atomically thin InSe seriously limits its practical applications. To develop an effective strategy to protect InSe, it is crucial to reveal the degradation mechanism at the atomic level. By employing density functional theory and ab initio molecular dynamics simulations, we provide an in-depth understanding of the oxidation mechanism of InSe. The defect-free InSe presents excellent stability against oxidation. Nevertheless, the Se vacancies on the surface can react with water and oxygen in air directly and activate the neighboring In–Se bonds on the basal plane for further oxidation, leading to complete degradation of InSe into oxidation products of In2O3 and elemental Se. Furthermore, we propose an efficient strategy to repair the Se vacancies by thiol chemistry. In this way, t...

The chemical functionalization is proven to be an effective and controllable approach to modify the properties of black phosphorus (BP), and improve the air-stability of BP and its nanoelectronic applications [Nat. Chem., 2016, 8, 597]. However, covalent functionalization of BP and related properties are poorly understood. Here we present a theoretical investigation on the electronic structure and transport property of chemically modified BP. Our calculations reveal that the molecule modification generates a rather flat energy band within the bandgap, which leads to a reduced hole mobility of BP. Alternatively, we propose to use polymers bonded to BP surface, aiming at a balance between functionality and carrier mobility. The polymer–BP composites preserve both electron and hole mobility of pristine BP. Meanwhile, the stability of polymer–BP composites in ambient condition is enhanced as well.