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Van der waal

Lijuan Zhang, Dazhi Li, Min Cheng, Yikui Du, Qihe Zhu
The ab initio and dispersion-corrected density functional theory (DFT) calculations of the van der Waals (vdW) clusters of cis and trans 3-fluoro-N-methylaniline-Arn (3FNMA-Arn) (n=1,2) predict that, for cis and trans 3FNMA-Ar1 clusters, the π-bound geometry with the Ar atom sitting over the ring is the global minimum in both neutral and cationic states, while for cis and trans 3FNMA-Ar2 clusters, the [π|π]-bound sandwich structure with two Ar ligands occupying nearly equivalent π-bound positions above and below the ring plane is the global minimum...
April 18, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Justyna Krupa, Maria Wierzejewska
Matrix isolation FTIR spectroscopy has been combined with quantum chemical calculations in the aim to characterize complexes of isothiocyanic acid HNCS with SO2. The geometries of the 1:1, 1:2 and 2:1 complexes were optimized at the MP2 and DFT (B3LYPD3) levels of theory with the 6-311++G(3df,3pd) basis set. Five different HNCS⋯SO2 structures of the 1:1 stoichiometry were optimized. Three of them involve a weak NH⋯O hydrogen bond whereas two other geometries are stabilized by van der Waals interactions of various types...
April 19, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Torsten Linker, Prashant Pavashe, Werner Fudickar
Carbohydrates carrying thiol groups at the C-2 position have been attached to gold nanoparticles (AuNP) with stereocenters in close proximity to the surface for the first time. Their configurations can be clearly distinguished by the tendency of particle aggregation. AuNP surface plasmon resonance (SPR), x-ray photoelectron spectroscopy (XPS), and IR spectroscopy indicate that the thiocarbohydrates replace citrate molecules at different rates causing aggregation and eventually precipitation. A quantitative formulation of this aggregation process shows that reactivities can vary by several magnitudes...
April 26, 2017: Chemistry: a European Journal
Cheng Gong, Lin Li, Zhenglu Li, Huiwen Ji, Alex Stern, Yang Xia, Ting Cao, Wei Bao, Chenzhe Wang, Yuan Wang, Z Q Qiu, R J Cava, Steven G Louie, Jing Xia, Xiang Zhang
The realization of long-range ferromagnetic order in two-dimensional van der Waals crystals, combined with their rich electronic and optical properties, could lead to new magnetic, magnetoelectric and magneto-optic applications. In two-dimensional systems, the long-range magnetic order is strongly suppressed by thermal fluctuations, according to the Mermin-Wagner theorem; however, these thermal fluctuations can be counteracted by magnetic anisotropy. Previous efforts, based on defect and composition engineering, or the proximity effect, introduced magnetic responses only locally or extrinsically...
April 26, 2017: Nature
Nicolas Leconte, Hakseong Kim, Ho-Jong Kim, Dong Han Ha, Kenji Watanabe, Takashi Taniguchi, Jeil Jung, Suyong Jung
Graphene bubbles are often formed when graphene and other layered two-dimensional materials are vertically stacked as van der Waals heterostructures. Here, we investigate how graphene bubbles and their related disorder impact the quantum transport behavior of graphene in the absence and presence of external magnetic fields. By combining experimental observations and numerical simulations, we find that the disorder induced by the graphene bubbles is mainly from p-type dopants and the charge transport in pristine graphene can be severely influenced by the presence of bubbles via long- and short-range scattering even with a small bubble-coverage of 2% and below...
April 26, 2017: Nanoscale
Alain C Tagne Kuate, Roger A Lalancette, F Jäkle
The synthesis of ferrocenylphosphine-borane adducts 1,2-fc(E)(PPh2·BH3) (E = SnR2R', HgX; 1,2-fc = 1,2-ferrocenediyl) that are substituted with organotin or organomercury Lewis acid moieties in ortho-position is presented. Several compounds that feature two ferrocenylphosphine-borane moieties bridged by Sn or Hg are also introduced. The products are fully characterized by multinuclear NMR spectroscopy, high-resolution MALDI-TOF mass spectrometry and elemental analysis. The attachment of the Lewis acid substituent to the same Cp ring of the ferrocene results in planar-chirality and the close proximity between the boron hydride group and the Lewis acid is expected to allow for agostic-type B-HE (E = Sn, Hg) interactions...
April 26, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
Shahid Sattar, Udo Schwingenschlögl
In this article, we study the electronic properties of graphene in contact with monolayer and bilayer PtSe2 using first-principles calculations. It turns out that there is no charge transfer between the components because of the weak van der Waals interaction. We calculate the work functions of monolayer and bilayer PtSe2 and analyze the band bending at the contact with graphene. The formation of an n-type Schottky contact with monolayer PtSe2 and a p-type Schottky contact with bilayer PtSe2 is demonstrated...
April 26, 2017: ACS Applied Materials & Interfaces
Alejandra I Martinez-Gonzalez, Ángel G Díaz-Sánchez, Laura A de la Rosa, Claudia L Vargas-Requena, Ismael Bustos-Jaimes, And Emilio Alvarez-Parrilla
The digestive enzymes-polyphenolic compounds (PCs) interactions behind the inhibition of these enzymes have not been completely studied. The existing studies have mainly analyzed polyphenolic extracts and reported inhibition percentages of catalytic activities determined by UV-Vis spectroscopy techniques. Recently, pure PCs and new methods such as isothermal titration calorimetry and circular dichroism have been applied to describe these interactions. The present review focuses on PCs structural characteristics behind the inhibition of digestive enzymes, and progress of the used methods...
April 22, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Mattia Sist, Carlo Gatti, Peter Nørby, Simone Cenedese, Hidetaka Kasai, Kenichi Kato, Bo B Iversen
The discovery of the ultra-high thermoelectric figure of merit of 2.6 in SnSe has drawn attention to other lead-free IV-VI orthorhombic semiconductors. GeSe has been predicted to possess thermoelectric performances comparable to SnSe. Here, a complete structural study is reported of GeSe with temperature by means of high-resolution synchrotron powder X-ray diffraction. In the orthorhombic phase, the evolution of the bond distances with temperature is shown to deviate significantly with respect to SnSe. Analysis of the chemical bonding within the Quantum Theory of Atoms in Molecules shows that GeSe is ionic with van der Waals interlayer interactions...
April 25, 2017: Chemistry: a European Journal
Jiunn-Woei Liaw, Wu-Chun Lin, Mao-Kuen Kuo
Plasmon-mediated coalescence of two nearby gold nanorods (NRs) suspended in water induced by the illumination of a linearly polarized (LP) light was studied theoretically. We analyzed the coupled optical forces and torques in terms of Maxwell's stress tensor upon two identical NRs irradiated by a LP plane wave using the multiple multipole method to estimate the optomechanical outcome. Numerical results show that the light-matter interaction can perform attraction or repulsion, depending on their initial configurations...
April 25, 2017: Scientific Reports
Yoichi Kobayashi, Hajime Okajima, Hikaru Sotome, Takeshi Yanai, Katsuya Mutoh, Yusuke Yoneda, Yasuteru Shigeta, Akira Sakamoto, Hiroshi Miyasaka, Jiro Abe
Delocalized biradicals have been extensively studied because of fundamental interests to singlet biradicals and several potential applications such as to two-photon absorption materials. However, many of the biradical studies only focus on the static properties of the rigid molecular structures. It is expected that the biradical properties of the delocalized biradicals are sensitive to the subtle changes of the molecular structures and their local environments. Therefore, the studies of the dynamic properties of the system will give further insight into stable radical chemistry...
April 28, 2017: Journal of the American Chemical Society
Zhao-Xin Lao, Yan-Lei Hu, Deng Pan, Ren-Yan Wang, Chen-Chu Zhang, Jin-Cheng Ni, Bing Xu, Jia-Wen Li, Dong Wu, Jia-Ru Chu
Long microchannels with thin walls, small width, and nanoholes or irregular shaped microgaps, which are similar to capillaries or cancerous vessels, are urgently needed to simulate the physiological activities in human body. However, the fabrication of such channels remains challenging. Here, microchannels with designable holes are manufactured by combining laser printing with line-contact capillary-force assembly. Two microwalls are first printed by femtosecond laser direct-writing, and subsequently driven to collapse into a channel by the capillary force that arises in the evaporation of developer...
April 25, 2017: Small
Claudia Ojeda-Aristizabal, Elton J G Santos, Seita Onishi, Aiming Yan, Haider Imad Rasool, Salman Kahn, Yinchuan Lv, Drew Latzke, Jairo Velasco, Michael F Crommie, Matthew Sorensen, Kenneth Gotlieb, Chiu-Yun Lin, Kenji Watanabe, Takashi Taniguchi, Alessandra Lanzara, Alex Zettl
Charge transfer at the interface between dissimilar materials is at the heart of electronics and photovoltaics. Here we study the molecular orientation, electronic structure, and local charge transfer at the interface region of C60 deposited on graphene, with and without supporting substrates such as hexagonal boron nitride. We employ ab initio density functional theory with van der Waals (vdW) interactions, and experimentally characterize interface devices using high-resolution transmission electron microscopy and electronic transport...
April 24, 2017: ACS Nano
Bess Vlaisavljevich, Johanna M Huck, Zeric Hulvey, Kyuho Lee, Jarad A Mason, Jeffrey B Neaton, Jeffrey R Long, Craig M Brown, Dario Alfè, Angelos Michaelides, Berend Smit
Small molecule binding in metal-organic frameworks (MOFs) can be accurately studied both experimentally and computationally, provided the proper tools are employed. Herein, we compare and contrast properties associated with guest binding by means of density functional theory (DFT) calculations using nine different functionals for the M2(dobdc) (dobdc4- = 2,5-dioxido,1,4-benzenedicarboxylate) series where M = Mg, Mn, Fe, Co, Ni, Cu, and Zn. Additionally, we perform Quantum Monte Carlo (QMC) calculations for one system to determine if this method can be used to assess the performance of DFT...
April 24, 2017: Journal of Physical Chemistry. A
Ran Tivony, Jacob Klein
Combining direct surface force measurements with in situ regulation of surface potential provides an exceptional opportunity for investigating and manipulating interfacial phenomena. Recently, we studied the interaction between gold and mica surfaces in water with no added salt, while controlling the metal potential, and found that the surface charge at the metal may vary, and possibly even change its sign, as it progressively approaches the (constant-charge) mica surface [Langmuir, 2015, 31(47), 12845-12849]...
April 24, 2017: Faraday Discussions
Morten N Gjerding, Mohnish Pandey, Kristian S Thygesen
Plasmonics currently faces the problem of seemingly inevitable optical losses occurring in the metallic components that challenges the implementation of essentially any application. In this work, we show that Ohmic losses are reduced in certain layered metals, such as the transition metal dichalcogenide TaS2, due to an extraordinarily small density of states for scattering in the near-IR originating from their special electronic band structure. On the basis of this observation, we propose a new class of band structure engineered van der Waals layered metals composed of hexagonal transition metal chalcogenide-halide layers with greatly suppressed intrinsic losses...
April 24, 2017: Nature Communications
Rosario C Sausa, Rose A Pesce-Rodriguez, Leah A Wingard, Pablo E Guzmán, Jesse J Sabatini
The mol-ecular structure of the title energetic compound, C8H6N4O8, is composed of two planar isoxazole rings and two near planar alkyl-nitrate groups (r.m.s deviation = 0.006 Å). In the crystal, the mol-ecule sits on an inversion center, thus Z' = 0.5. The dihedral angle between the isoxazole ring and the nitrate group is 69.58 (8)°. van der Waals contacts dominate the inter-molecular inter-actions. Inversion-related rings are in close slip-stacked proximity, with an inter-planar separation of 3.101 (3) Å [centroid-centroid distance = 3...
April 1, 2017: Acta Crystallographica. Section E, Crystallographic Communications
Shuling Xiong, Shusen Chen, Shaohua Jin
Dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) is a newly synthesized energetic material with excellent comprehensive properties. Cyclotrimethylenetrinitramine (RDX) is currently one of the most widely used energetic materials in the world. TKX-50 and RDX supercell models and TKX-50/RDX cocrystal model were constructed based on their crystal cell parameters and the formation mechanism of cocrystal, respectively, then they were simulated by molecular dynamics (MD) simulations. The maximum trigger bond (NNO2) length(Lmax), binding energy (Ebind), radial distribution function (RDF), cohesive energy density(CED) and mechanical properties were simulated at different temperatures based on the simulated equilibrium structures of the models...
March 19, 2017: Journal of Molecular Graphics & Modelling
Fengcheng Wu, Timothy Lovorn, A H MacDonald
Moiré patterns are common in van der Waals heterostructures and can be used to apply periodic potentials to elementary excitations. We show that the optical absorption spectrum of transition metal dichalcogenide bilayers is profoundly altered by long period moiré patterns that introduce twist-angle dependent satellite excitonic peaks. Topological exciton bands with nonzero Chern numbers that support chiral excitonic edge states can be engineered by combining three ingredients: (i) the valley Berry phase induced by electron-hole exchange interactions, (ii) the moiré potential, and (iii) the valley Zeeman field...
April 7, 2017: Physical Review Letters
Natarajan Sathiyamoorthy Venkataramanan, Ambigapathy Suvitha
The encapsulation of nucleobases, inside CB7 has gained prominence due to its use as anticancer and antiviral drugs. With this respect, the nonconvalent interactions exists in the nucleobases encapsulated inside the CB7 cavity have been analyzed employing the dispersion corrected density functional theory. The CBn cavity has the ability to encapsulate two guest nucleobases molecules, when they are aligned in parallel configuration. The computed association energy using the two and three body correction method computed at B3LYP-D3 level is close to the experimental estimate...
April 21, 2017: Journal of Physical Chemistry. B
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