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Atomic clusters

Hum N Bandari, Xinyou Ma, Amit Kumar Paul, Philip Smith, William Louis Hase
In this work a Particle Swarm Optimization (PSO) algorithm was used to fit an analytic potential energy function to I-(H2O) intermolecular potential energy curves calculated with DFT/B97-1 theory. The analytic function is a sum of two-body terms, each written as a generalized sum of Buckingham and Lennard-Jones terms with only six parameters. Two models were used to describe the two-body terms between I- and H2O: a 3-site model H2O; and a 4-site model including a ghost atom. The fits are compared with those obtained with a genetic/non-linear least-squares algorithm...
January 18, 2018: Journal of Chemical Theory and Computation
David James Coughtrie, Robin Giereth, Daniel Kats, Hans-Joachim Werner, Andreas Köhn
Internally contracted multireference coupled cluster (icMRCC) theory is embedded within multireference perturbation theory (MRPT) to calculate energy differences in large strongly correlated systems. The embedding scheme is based on partitioning the orbital spaces of a complete active space self consistent field (CASSCF) wave function, with the truncated virtual space constructed by transforming selected projected atomic orbitals (PAOs). MRPT is applied to the environment using a subtractive embedding approach, that also allows for multilayer embedding...
January 18, 2018: Journal of Chemical Theory and Computation
Jiri Brabec, Jakub Lang, Masaaki Saitow, Jiri Pittner, Frank Neese, Ondrej Demel
This article reports development of a local variant of Mukherjee's state specific multireference coupled cluster method based on the domain-based pair natural orbital approach (DLPNO-MkCC). The current implementation is restricted to connected single and double excitations and model space with up to biexcited references. The performance of the DLPNO-MkCCSD was tested on calculations of tetramethyleneethane. The results show that above 99.9% of correlation energy was recovered, with respect to the conventional MkCC method...
January 18, 2018: Journal of Chemical Theory and Computation
Jia-Wei Liu, Lei Feng, Haifeng Su, Zhi Wang, Quan-Qin Zhao, Xingpo Wang, Chen-Ho Tung, Di Sun, Lan-Sun Zheng
Although there has been an upsurge of interest in anisotropic assembly of inorganic nanoparticles, atomically precise self-assembly of anisotropic (nonspherical) high-nuclearity metal clusters is extremely rare. Herein, we presented two novel silver nanoclusters, Ag52 (SD/Ag23) and Ag76 (SD/Ag24), which are interiorly templated by five MoO42- and a pair of Mo6O228- anions, respectively, and co-protected by bridging RSH and terminal diphosphine ligands exteriorly. Regiospe-cific distribution diphosphine ligands on the surface and the arrangement of multiple molybdate templates within the nanoclusters synergetically tailor their shapes to anisotropic oblate spheroid and elongated rod, respectively, as opposed to isotropic nanospheres...
January 18, 2018: Journal of the American Chemical Society
Chi Zhang, Lei Xie, Yuanqi Ding, Chunxue Yuan, Wei Xu
From the interplay between high-resolution scanning tunneling microscopy imaging/manipulations and density functional theory calculations, we display the hierarchical formation of supramolecular networks by codeposition of 9eG molecules and Fe atoms on Au(111) based on the flexible coordination bonds (the adaptability and versatility in the coordination modes). In the first step, homochiral islands composed of homochiral G4Fe2 motifs are formed; and then in the second step, thermal treatment results in the transformation into the porous networks composed of heterochiral G4Fe2 motifs with the ratio of the components being constant...
January 18, 2018: Physical Chemistry Chemical Physics: PCCP
Xiaotian Zhang, Tanushree H Choudhury, Mikhail Chubarov, Yu Xiang, Bhakti Jariwala, Fu Zhang, Nasim Alem, Gwo-Ching Wang, Joshua A Robinson, Joan M Redwing
A multi-step diffusion-mediated process was developed to control the nucleation density, size and lateral growth rate of WSe2 domains on c-plane sapphire for the epitaxial growth of large area monolayer films by gas source chemical vapor deposition (CVD). The process consists of an initial nucleation step followed by an annealing period in H2Se to promote surface diffusion of tungsten-containing species to form oriented WSe2 islands with uniform size and controlled density. The growth conditions were then adjusted to suppress further nucleation and laterally grow the WSe2 islands to form a fully coalesced monolayer film in less than one hour...
January 17, 2018: Nano Letters
R Smith, Tz Kokalova, C Wheldon, J E Bishop, M Freer, N Curtis, D J Parker
Excited states in certain atomic nuclei possess an unusual structure, where the dominant degrees of freedom are those of α clusters rather than individual nucleons. It has been proposed that the diffuse 3α system of the ^{12}C Hoyle state may behave like a Bose-Einstein condensate, where the α clusters maintain their bosonic identities. By measuring the decay of the Hoyle state into three α particles, we obtained an upper limit for the rare direct 3α decay branch of 0.047%. This value is now at a level comparable with theoretical predictions and could be a sensitive probe of the structure of this state...
September 29, 2017: Physical Review Letters
Xiaofan Xu, Wei Wang, Dongliang Liu, Dandan Hu, Tao Wu, Xianhui Bu, Pingyun Feng
The cubic ZnS structure type and the size-dependent properties of related nanoparticles are of both fundamental and technological importance. Yet, it remains a challenge to synthesize large atom-precise clusters of this structure type. Currently, only supertetrahedral clusters with 4, 10, 20, and 35 metal sites (denoted as T2, T3, T4, and T5, respectively) are known. Because the synthesis of T5 in 2002, numerous synthetic efforts targeting larger clusters only resulted in T2-T5 clusters in various compositions and intercluster connectivity, with T6 (56 metal and 84 anion sites) being elusive...
January 16, 2018: Journal of the American Chemical Society
Silke Wolf, Wim Klopper, Claus Feldmann
The germanium-iron cluster Ge12{Fe(CO)3}8(μ-I)4 was prepared by reacting GeI4 and Fe2(CO)9 in [BMIm]Cl/AlCl3 as ionic liquid (BMIm: 1-butyl-3-methylimidazolium). The cluster contains a Ge12Fe8 metal core consisting of a central Ge4 rectangle, two Ge2 pairs, and four single Ge atoms. These Ge units are interconnected by Fe atoms to a real Ge-Fe cluster. According to DFT calculations, Hund's localization criterion is fulfilled for the whole cluster if we assume three different atomic charges on the Ge4, Ge2, and Ge units...
January 16, 2018: Chemical Communications: Chem Comm
Michael G S Londesborough, Jiří Dolanský, Tomáš Jelínek, John D Kennedy, Ivana Císařová, Robert D Kennedy, Daniel Roca-Sanjuán, Antonio Francés-Monerris, Kamil Lang, William Clegg
Reaction of anti-B18H221 with pyridine in neutral solvents gives sparingly soluble B16H18-3',8'-Py23a as the major product (ca. 53%) and B18H20-6',9'-Py22 (ca. 15%) as the minor product, with small quantities of B18H20-8'-Py 4 (ca. 1%) also being formed. The three new compounds 2, 3a and 4 are characterized by single-crystal X-ray diffraction analyses and by multinuclear multiple-resonance NMR spectroscopy. Compound 2 is of ten-vertex nido:ten-vertex arachno two-atoms-in-common architecture, long postulated for a species with borons-only cluster constitution, but previously elusive...
January 15, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Anna Carolina Schneider Alves, Reinaldo Antonio Dias, Luciano Porto Kagami, Gustavo Machado das Neves, Fernando Cidade Torres, Vera Lucia Eifler-Lima, Ivone Carvalho, Carolina de Miranda Silva, Daniel Fabio Kawano
For more than 40 years, the fluid mosaic model of cellular membranes have supported our vision of an inert lipid bilayer containing membrane protein receptors that are randomly hit by extracellular molecules to trigger intracellular signaling events. However, the notion that compartmentalized cholesterol- and sphingomyelin-rich membrane microdomains (known as lipid rafts) spatially arrange receptors and effectors to promote kinetically favorable interactions necessary for the signal transduction sounds much more realistic...
January 10, 2018: Current Medicinal Chemistry
Yubiao Niu, Philomena Schlexer, Bela Sebok, Ib Chorkendorff, Gianfranco Pacchioni, Richard E Palmer
Au nanoparticles represent the most remarkable example of a size effect in heterogeneous catalysis. However, a major issue hindering the use of Au nanoparticles in technological applications is their rapid sintering. We explore the potential of stabilizing Au nanoclusters on SiO2 by alloying them with a reactive metal, Ti. Mass-selected Au/Ti clusters (400 000 amu) and Au2057 clusters (405 229 amu) were produced with a magnetron sputtering, gas condensation cluster beam source in conjunction with a lateral time-of-flight mass filter, deposited onto a silica support and characterised by XPS and LEIS...
January 12, 2018: Nanoscale
L Schiavo, S De Nicola, G Carotenuto
Pd(0) is able to catalyze oxygen-involving reactions because of its capability to convert molecular oxygen to the very reactive atomic form. Consequently, the embedding of a little amount of Pd(0) clusters in polymeric phases can be technologically exploited to enhance the incineration kinetic of these polymers. The effect of nanostructuration on the Pd(0) catalytic activity in the polymer incineration reaction has been studied using poly(N-vinyl-2-pyrrolidone) ([Formula: see text] = 10,000 gmol-1) as polymeric model system...
January 11, 2018: Nanoscale Research Letters
Junko Kajimura, Heather E Lynch, Susan Geyer, Benjamin French, Mika Yamaoka, Ivo D Shterev, Gregory D Sempowski, Seishi Kyoizumi, Kengo Yoshida, Munechika Misumi, Waka Ohishi, Tomonori Hayashi, Kei Nakachi, Yoichiro Kusunoki
Previous immunological studies in atomic bomb survivors have suggested that radiation exposure leads to long-lasting changes, similar to immunological aging observed in T-cell-adaptive immunity. However, to our knowledge, late effects of radiation on dendritic cells (DCs), the key coordinators for activation and differentiation of T cells, have not yet been investigated in humans. In the current study, we hypothesized that numerical and functional decreases would be observed in relationship to radiation dose in circulating conventional DCs (cDCs) and plasmacytoid DCs (pDCs) among 229 Japanese A-bomb survivors...
January 2018: Radiation Research
Saravanan Govindaraju, Arunkumar Rengaraj, Roshini Arivazhagan, Yun-Suk Huh, Kyusik Yun
Curcumin-conjugated gold clusters (CUR-AuNCs) were synthesized using a "green" procedure and utilized as an anticancer and a bioimaging agent. Curcumin is a well-known anticancer agent, which forms a cluster when reacting with a gold precursor under mild alkali condition. A fluorescence spectroscopy analysis showed that the CUR-AuNCs emitted red fluorescence (650 nm) upon visible light (550) irradiation. Fourier transform infrared spectroscopy analysis confirmed the stretching and bending nature between the gold atoms and curcumin...
January 11, 2018: Bioconjugate Chemistry
Petr Melichar, Drahomír Hnyk, Jindřich Fanfrlík
This paper presents a systematic study of multicenter and classical bonding on a broad series of experimentally known heteroboranes covering closo, nido, arachno and hypho types of cages with incorporated tetrel, pnictogen or chalcogen heterovertices up to the third-row elements. The nature of bonding is studied using a novel quantum-chemical tool, the intrinsic atomic/bond orbital (IAO/IBO) approach, which provides a direct connection between quantum chemistry and chemical concepts. We also discuss how the computed IBO properties are related to molecular observables such as interatomic distances, molecular electrostatic potential surfaces and dipole moments...
January 11, 2018: Physical Chemistry Chemical Physics: PCCP
Wenbo Xin, Igor M De Rosa, Peiyi Ye, Joseph Severino, Chao Li, Xunqian Yin, Mark S Goorsky, Larry Carlson, Jenn-Ming Yang
Assembling Au nanocrystals with tunable dimensions and shapes on graphene templates has attracted increasing attention recently. However, directly growing anisotropic Au nanobelts on a graphene support has been rarely reported. Here, a facile, one-pot, and surfactant-free route is demonstrated to synthesize well-defined Au nanobelts with the induction of a multilayer graphene (mlG) template. The obtained Au nanobelts are single-crystalline with a preferable (111) orientation. More importantly, their structural evolution starting from Au clusters is systematically investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM)...
January 11, 2018: Nanoscale
Chien-Chang Chen, Hung-Hui Juan, Meng-Yuan Tsai, Henry Horng-Shing Lu
By introducing the methods of machine learning into the density functional theory, we made a detour for the construction of the most probable density function, which can be estimated by learning relevant features from the system of interest. Using the properties of universal functional, the vital core of density functional theory, the most probable cluster numbers and the corresponding cluster boundaries in a studying system can be simultaneously and automatically determined and the plausibility is erected on the Hohenberg-Kohn theorems...
January 11, 2018: Scientific Reports
Jonas Franz, Jonas Grünebaum, Marcus Schäfer, Dennis Mulac, Florian Rehfeldt, Klaus Langer, Armin Kramer, Christoph Riethmüller
Symmetry is rarely found on cellular surfaces. An exception is the brush border of microvilli, which are essential for the proper function of transport epithelia. In a healthy intestine, they appear densely packed as a 2D-hexagonal lattice. For in vitro testing of intestinal transport the cell line Caco-2 has been established. As reported by electron microscopy, their microvilli arrange primarily in clusters developing secondly into a 2D-hexagonal lattice. Here, atomic force microscopy (AFM) was employed under aqueous buffer conditions on Caco-2 cells, which were cultivated on permeable filter membranes for optimum differentiation...
2018: PloS One
U Reeta Felscia, Beulah J M Rajkumar, Monickaraj Nidya, Pranitha Sankar
Investigation on the electrostatic interactions between histidine and silver have been analysed using Density Functional Theory (DFT). Variations in the structural parameters were identified to be significant at those atoms of histidine near the silver cluster. Shifting of frontier molecular orbitals, reduction in bandgap, molecular electrostatic potential(MEP) and the overlap of Natural Bond Orbitals(NBO) between silver and histidine have been theoretically calculated. The results confirm the redistribution of charges consequent to the process of adsorption...
January 10, 2018: Journal of Physical Chemistry. A
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