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Oak Ridge, TN, United States

Parkhill J.A.,Lawrence Berkeley National Laboratory | Head-Gordon M.,Chemical Science Division
Journal of Chemical Physics | Year: 2010

Paired, active-space treatments of static correlation are augmented with additional amplitudes to produce a hierarchy of parsimonious and efficient cluster truncations that approximate the total energy. The number of parameters introduced in these models grow with system size in a tractable way: two powers larger than the static correlation model it is built upon: for instance cubic for the models built on perfect pairing, fourth order for a perfect quadruples (PQ) reference, and fifth order for the models built on perfect hextuples. These methods are called singles+doubles (SD) corrections to perfect pairing, PQ, perfect hextuples, and two variants are explored. An implementation of the SD methods is compared to benchmark results for F2 and H2 O dissociation problems, the H4 and H8 model systems, and the insertion of beryllium into hydrogen. In the cases examined even the quartic number of parameters associated with PQSD is able to provide results which meaningfully improve on coupled-cluster singles doubles (CCSD) (which also has quartic amplitudes) and compete with existing multi-reference alternatives. © 2010 American Institute of Physics.

Bugaris D.E.,Northwestern University | Copping R.,Chemical Science Division | Tyliszczak T.,Lawrence Berkeley National Laboratory | Shuh D.K.,Chemical Science Division | Ibers J.A.,Northwestern University
Inorganic Chemistry | Year: 2010

The compound La2U2Se9 was obtained in high yield from the stoichiometric reaction of the elements in an Sb 2Se3 flux at 1123 K. The compound, which crystallizes in a new structure type in space group Pmma of the orthorhombic system, has a three-dimensional structure with alternating U/Se and La/Se layers attached via three independent, infinite polyselenide chains. The U atom has a monocapped square antiprismatlc coordination of Se atoms, whereas one La atom is bicapped square prismatic and the other La atom is trigonal prismatic. La 2U2Se9 displays an antiferromagnetic transition at TN = 5 K; above 50 K, the paramagnetic behavior can be fit to the Curie-Weiss law, yielding a μeff of 3.10(1) μB/U. The low-temperature specific heat of La2U2Se9 exhibits no anomalous behavior near the Néel temperature that might indicate long-range magnetic ordering or a phase transition. X-ray absorption near-edge structure (XANES) spectra have confirmed the assignment of formal oxidation states of +III for lanthanum and +IV for uranium in La 2U2Se9. ©2010 American Chemical Society.

Feng G.,Vanderbilt University | Jiang D.-E.,Chemical Science Division | Cummings P.T.,Vanderbilt University | Cummings P.T.,Oak Ridge National Laboratory
Journal of Chemical Theory and Computation | Year: 2012

Recent experiments have revealed that onion-like carbons (OLCs) offer high energy density and charging/discharging rates when used as the electrodes in supercapacitors. To understand the physical origin of this phenomenon, molecular dynamics simulations were performed for a room-temperature ionic liquid near idealized spherical OLCs with radii ranging from 0.356 to 1.223 nm. We find that the surface charge density increases almost linearly with the potential applied on electric double layers (EDLs) near OLCs. This leads to a nearly flat shape of the differential capacitance versus the potential, unlike the bell or camel shape observed on planar electrodes. Moreover, our simulations reveal that the capacitance of EDLs on OLCs increases with the curvature or as the OLC size decreases, in agreement with experimental observations. The curvature effect is explained by dominance of charge overscreening over a wide potential range and increased ion density per unit area of electrode surface as the OLC becomes smaller. © 2012 American Chemical Society.

Singh R.K.,Chemical Science Division | Kukrety A.,Chemical Science Division | Saxena R.C.,Chemical Science Division | Thakre G.D.,Tribology Division | And 2 more authors.
Industrial and Engineering Chemistry Research | Year: 2016

Two novel triazine Schiff base-based cationic gemini surfactants namely N,N′-bis{(p-(N,N,N-tetradecyldimethylammonium bromide)benzylidene} 6-methyl-1,3,5-triazine-2,4-diamine (14-MTR-14) and N,N′-bis{(p-(N,N,N-tetradecyldimethylammonium bromide)benzylidene} 6-phenyl-1,3,5-triazine-2,4-diamine (14-PTR-14) were synthesized following the two-step reaction. First the intermediate adduct was synthesized by reaction of the 4-(dimethylamino)benzaldehyde with 1-bromotetradecane. In the second step, the germinal surfactants 14-MTR-14 and 14-PTR-14 were synthesized by imine coupling with this intermediate adduct with 6-methyl-1,3,5-triazine-2,4-diamine and 6-phenyl-1,3,5-triazine-2,4-diamine, respectively. Both were characterized using elemental analysis (CHN), infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetry (TG). The compounds were then evaluated as anticorrosive and lubricity improver additive in polyol lube base oil. Both the surfactants show the similar anticorrosive activities. The antiwear and antifriction characteristics were estimated in terms of average wear scar diameter (AWSD) and average friction coefficient using a four ball test following ASTM D4172B. It was found that the 14-MTR-14 is comparatively more effective than 14-PTR-14. 14-MTR-14 reduces the AWSD of the polyol from 690 to 575.83 μm while the average friction coefficient decreases from 0.110 to 0.082 at 4000 ppm doping concentration. © 2016 American Chemical Society.

Schantz M.M.,U.S. National Institute of Standards and Technology | Cleveland D.,U.S. National Institute of Standards and Technology | Heckert N.A.,U.S. National Institute of Standards and Technology | Kucklick J.R.,Chemical Science Division | And 11 more authors.
Analytical and Bioanalytical Chemistry | Year: 2016

Abstract: Two new Standard Reference Materials (SRMs), SRM 2786 Fine Particulate Matter (<4 μm) and SRM 2787 Fine Particulate Matter (<10 μm) have been developed in support of the US Environmental Protection Agency’s National Ambient Air Quality Standards for particulate matter (PM). These materials have been characterized for the mass fractions of selected polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs, brominated diphenyl ether (BDE) congeners, hexabromocyclododecane (HBCD) isomers, sugars, polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) congeners, and inorganic constituents, as well as particle-size characteristics. These materials are the first Certified Reference Materials available to support measurements of both organic and inorganic constituents in fine PM. In addition, values for PAHs are available for RM 8785 Air Particulate Matter on Filter Media. As such, these SRMs will be useful as quality control samples for ensuring compatibility of results among PM monitoring studies and will fill a void to assess the accuracy of analytical methods used in these studies. [Figure not available: see fulltext.] © 2016 Springer-Verlag Berlin Heidelberg (outside the USA)

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