1,978 research outputs found
Ab initio calculations predicting the existence of an oxidized calcium dihydrogen complex to store molecular hydrogen in densities up to 100 g/L
No full textWe propose a system that can store molecular hydrogen in densities up to similar to 100 g/L. Our ab initio calculations predict the existence of an oxidized calcium dihydrogen complex, which holds up to eight H(2), i.e., Ca(ion)(H(2))(8). The dihydrogen binding to the Ca is via a weak electron-donation mechanism from the occupied H(2) sigma orbital to the unoccupied, but bound, Ca 3d orbitals. Because of the high concentration of the hydrogen in such complexes, even in calcium-intercalated pillared graphite, one can obtain reversible hydrogen storage denser than that of liquid hydrogen, 70 g/L
Effect of spin state on the dihydrogen binding strength to transition metal centers in metal-organic frameworks
No full textIn several recent experimental studies, it has been found that exposed transition metal (TM) sites in metal-organic frameworks (MOFs) yield the largest binding to H-2 by about 10 kJ/mol. However, this binding is significantly smaller than what has been observed in the so-called Kubas molecules, also with exposed metal sites. Our ab initio calculations quantitatively account for the experimental findings and further show that the splitting and occupation of the spin orbitals in the MOF systems are the reasons for their unexpected small binding energies. We predict that the binding energy to H-2 in the MOF systems can be tuned between 10 and 50 kJ/mol by using early TM elements, namely, Sc, Ti, V, Cr, and Mn
Accurate and efficient calculation of van der Waals interactions within density functional theory by local atomic potential approach
No full textDensity functional theory (DFT) in the commonly used local density or generalized gradient approximation fails to describe van der Waals (vdW) interactions that are vital to organic, biological, and other molecular systems. Here, we propose a simple, efficient, yet accurate local atomic potential (LAP) approach, named DFT+LAP, for including vdW interactions in the framework of DFT. The LAPs for H, C, N, and O are generated by fitting the DFT+LAP potential energy curves of small molecule dimers to those obtained from coupled cluster calculations with single, double, and perturbatively treated triple excitations, CCSD(T). Excellent transferability of the LAPs is demonstrated by remarkable agreement with the JSCH-2005 benchmark database [P. Jurecka Phys. Chem. Chem. Phys. 8, 1985 (2006)], which provides the interaction energies of CCSD(T) quality for 165 vdW and hydrogen-bonded complexes. For over 100 vdW dominant complexes in this database, our DFT+LAP calculations give a mean absolute deviation from the benchmark results less than 0.5 kcal/mol. The DFT+LAP approach involves no extra computational cost other than standard DFT calculations and no modification of existing DFT codes, which enables straightforward quantum simulations, such as ab initio molecular dynamics, on biomolecular systems, as well as on other organic systems. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2992078
Electronic, optical, and mechanical properties of superhard cold-compressed phases of carbon
No full textBy means of standard and hybrid density functional theory, we analyzed the electronic, optical, and mechanical properties of the two discovered superhard orthorhombic (W) and monoclinic (M) phases of carbon, synthesized by cold compression. We demonstrated that both phases exhibit a transparent insulating behaviour with indirect band gaps of about 5.4 eV (W) and 4.5 eV (M), and highly isotropic optical spectra, substantially different to those of the related body centered tetragonal C-4 phase. The analysis of the elastic constants and Vickers hardness confirmed that these phases are as hard as the second hardest material c-BC2N (C) 201/ American Institute of Physics. [doi:10.1063/1.3610996
Fluorescent Organic Nanoparticles of Benzofuran-Naphthyridine Linked Molecules: Formation and Fluorescence Enhancement in Aqueous Media
No full textStrain-driven onset of nontrivial topological insulating states in Zintl Sr2X compounds (X = Pb, Sn)
No full textWe explore the topological behavior of the binary Zintl phase of the alkaline-earth-metal-based compounds Sr2Pb and Sr2Sn using both standard and hybrid density functional theory. It is found that Sr2Pb lies on the verge of a topological instability which can be suitably tuned through the application of a small uniaxial expansion strain (>3%). The resulting nontrivial topologically insulating state displays well-defined metallic states in the Sr2Pb(010) surface, whose evolution is studied as a function of the film thickness
Stability and water-resistance of humidity sensors using crosslinked and quaternized polyelectrolytes films
No full textImpedance-type humidity sensors using crosslinked and quaternized polyelectrolytes films were fabricated by dip-coating method, and their electrical and humidity-sensing properties have been investigated in the range of relative humidity (33-95% RH). The stability of these sensors was evaluated by exposing the sensors to various environments such as placing them in water and exposure to normal ambient for extended periods. The sensor was durable even after soaking in water for 1000 min. When the sensors were exposed to 80 degrees C and 100% RH for 24h, the sensors still showed almost three orders of change, exhibited good stability at high humidity and high temperature. Surface morphology of the sensors were also measured and estimated at different conditions. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved
Macro-scale decarbonisation of tourism: insights from Australia
No full textGovernments and businesses have pledged to rapidly decarbonise tourism to achieve net-zero by 2050. While mitigation initiatives are implemented by individual businesses, destination managers need information to track sectoral mitigation progress and identify areas that require policy interventions. To support evidence-based tourism climate decision making, this study proposes a decomposition framework that assesses changes of tourism emissions based on Intergovernmental Panel on Climate Change’s (IPCC) and International Energy Agency’s (IEA) net-zero macro-scale mitigation strategies. This framework has the capacity to track and benchmark tourism mitigation progress against milestones. A case study of Australia is used to demonstrate the approach, showing that Australia’s tourism system is not on track to net-zero, even though progress has been made on four out of six macro-scale indicators. Barriers to reaching net-zero are implied in continued growth of air transport and visitor spending, as well as the high carbon content of electricity used in the country. Results have global relevance, as they show that most countries will have to reduce emissions through a combination of government-led and destination-based strategies.Full Tex
Isomorphisms of character rings
No full textLet G and H be finite groups. It is proves that any ring isomorphism between character rings of G and H implies a perfect isometry between them, which is also a ring isomorphism.MathematicsSCI(E)2ARTICLE2161-1642
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