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In this study, a terpyridyl derivative 2-(6-(pyridin-2-yl)-4-(4-((E)-2-(pyridin-4-yl)-vinyl)phenyl)pyridin-2-yl)pyridine (abbreviated as PYTPY) has been designed and prepared with an A–π–A architecture (A = electron acceptor), whose spontaneous aggregation style can be triggered by different external conditions. Mathematical modelling through time dependent density functional theory (TD-DFT) provides a quantitative understanding of the equilibrium molecular geometries at the aggregated state between adjacent PYTPY molecules with addition of different additives, such as water, H+, and Ag+ ions. The vertical electronic excitations and the related UV-vis absorbing character of PYTPY under different conditions were also forecasted, which was verified by the examined absorption spectra. Our method of calculating intermolecular interactions between adjacent molecules and predicting spontaneous aggregation style and absorption performance under an external environment is generally applicable to design and create other functional organic materials. [ABSTRACT FROM AUTHOR]

Hexagonal monolayer AlN (h‐mAlN) is an indirect wide‐gap semiconductor and is attractive for use in optoelectronic devices. Herein, first‐principles calculations are performed to study the electronic, vibrational, elastic, and piezoelectric properties of H and F‐functionalized AlN sheets. The results indicate that the H‐/F‐functionalized (FAlNH) and fully H‐functionalized (HAlNH) sheets are thermodynamically and dynamically stable. FAlNH is a direct bandgap material while HAlNH is still an indirect one. The F(H) atoms in F(H)AlNH bonded with Al act as electron acceptors whereas the H atoms bonded with N are electron donors. Some vibrational modes of these two functionalized systems differ significantly although their structures are similar. Functionalization with the H and F atoms reduces the elastic constants considerably and alters the mechanical performances of both systems. The in‐plane piezoelectric constants of the FAlNH (HAlNH) sheet increase (decrease) surprisingly to about three times (one‐third) that of h‐mAlN. However, the work functions of both systems are enhanced notably. The study provides useful information for modulating the intrinsic properties of h‐mAlN for possible applications. [ABSTRACT FROM AUTHOR]

Non-stoichiometric transition metal chalcogenides often have unexpectedly good semiconducting properties. In this paper, we focus on the seeking of potential semiconducting material in the ReSe system. The global and unbiased crystal structure searches were systematically conducted on ReSe material, using the advanced crystal structure prediction algorithms combined with the density functional theory. Three novel structures of ReSe were discovered within different pressures regions. The phase diagram of ReSe material was then constructed at pressure up to 200 GPa and temperature up to 2500 K, based on the quasi-harmonic approximation. We found ReSe possesses the trigonal P 3 ¯ m 1 symmetric structure at ambient pressure. Under further compression, it transits to the orthorhombic Pmmn structure at 87 GPa and then to the cubic P m 3 ¯ m structure at 129 GPa. The three new structures are all mechanically and thermodynamically stable within corresponding pressures regions. The low-pressure P 3 ¯ m 1 -ReSe manifests good semiconducting properties with the band gap of 0.162 eV, while the two high-pressure allotropes have metallic characteristics. The mechanical properties analyses suggest that special attention should be paid on the brittleness of the P 3 ¯ m 1 -ReSe structure, when it is used at high-stress conditions. This study sheds considerable light on the new structures and properties of the non-stoichiometric transition metal chalcogenides ReSe for future synthesis and further investigation. [ABSTRACT FROM AUTHOR]

By performing first-principle quantum transport calculations, we investigated the effects of the edge types and edge defects on the electronic and transport properties of phosphorene nanoribbons (PNRs). The calculated band structures show the PNRs with the zigzag and cliff edges are all metallic. The conductance of the cliff phosphorene nanoribbon (CPNR) is higher than that of the zigzag phosphorene nanoribbon (ZPNR). The low bias negative differential resistance behavior is only found in the ZPNR and the peak-to-valley current ratio is up to 10 2 . More over, we found the carrier transport channels under low bias of ZPNR and CPNR mainly locate on the edges. The current-voltage characteristics show the defects induced by removing the phosphorus atoms from the edge can decrease the conductance of the ZPNR and CPNR obviously. The low bias negative differential resistance behavior of the ZPNR also can be weakened or removed by the edge defects. [ABSTRACT FROM AUTHOR]

By applying nonequilibrium Green's functions in combination with the density-functional theory, we investigate the electron transport properties of the salicylideneaniline molecule sandwiched between two armchair graphene nanoribbon (AGNR) electrodes. It shows that the width of the AGNR electrodes plays a significant role in the transport properties of the salicylideneaniline molecular junctions. The current–voltage characteristics of the salicylideneaniline molecule sandwiched between 8AGNR electrodes can perform a stable conductance switching behavior at the bias region [1.2 V, 1.6 V] when the molecule translates between the trans -enol form and the trans -keto form. When the electrodes change to 7AGNR, a remarkable negative differential resistance behavior can be found in the salicylideneaniline molecular device at the trans -keto form. That means the salicylideneaniline molecule can perform different functions when it connects to the different AGNR electrodes. [ABSTRACT FROM AUTHOR]

ZrBeSi is the prototype of the ZrBeSi‐type of crystals, but its fundamental properties have not been well studied till now. In this work, a systematic study on the electronic, elastic, and vibrational properties of ZrBeSi under zero and high pressures has been performed by first‐principles calculation. Calculated electronic properties indicate that ZrBeSi is metallic dictated mainly by the Zr 4d state. Its metallicity weakens as the pressure increases. Studies reveal that sp2 hybridization exists in the Be atoms and their 2p orbitals accept electrons from the Zr atoms, leading them to have an unusual negative valency. Calculated elastic properties imply that ZrBeSi is mechanically stable but anisotropic up to 175 GPa. It has a bulk modulus of 144.4 (142.5) GPa deduced from the third‐order Birch–Murnaghan equation of state (elastic constants) at 0 GPa. Its elastic moduli and elastic anisotropy increase with the rising pressure. Group theory analysis unveils that there are six infrared‐active and four Raman‐active modes at the Brillouin zone center of ZrBeSi. The vibrational patterns of these modes are presented and discussed. Studies further reveal that the frequencies of these modes increase with the rising pressure. [ABSTRACT FROM AUTHOR]