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Journal of Chemical Physics

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https://www.readbyqxmd.com/read/30089394/tic-and-tin-supported-platinum-monolayer-as-high-performance-catalysts-for-co-oxidation-a-dft-study
#1
Yan Wang, Zongxian Yang
The reactivity toward CO oxidation of Pt monolayer supported on TiC(001) and TiN(001) is studied by using empirical dispersion-corrected density functional theory calculations. A number of possible reaction pathways for CO oxidation, including the Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms, between adsorbed O2 and CO molecules considering the cases that the adsorbed O2 dissociates first or directly reacts with CO. It is found that the dissociation adsorption of O2 molecules as the initial step is more favorable with lower activation barriers compared with the direct reaction mode...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089393/communication-dielectric-properties-of-condensed-systems-composed-of-fragments
#2
Ding Pan, Marco Govoni, Giulia Galli
The dielectric properties of molecules and nanostructures are usually modified in a complex manner, when assembled into a condensed phase. We propose a first-principles method to compute polarizabilities of sub-entities of solids and liquids, which accounts for multipolar interactions at all orders and is applicable to semiconductors and insulators. The method only requires the evaluation of induced fields in the condensed phase, with no need of multiple calculations for each constituent. As an example, we present results for the molecular polarizabilities of water in a wide pressure and temperature range...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089392/thermodynamics-of-small-systems-with-conformational-transitions-the-case-of-two-state-freely-jointed-chains-with-extensible-units
#3
Manon Benedito, Stefano Giordano
Several experimental methods are usually applied for stretching single molecules and provide valuable insights about the static and dynamic responses induced by externally applied forces. This analysis is even more important for macromolecules exhibiting conformational transitions, thereby corresponding to folding/unfolding processes. With the aim of introducing the statistical mechanics of such phenomena, we apply here the spin variables approach based on a set of discrete quantities able to identify the folded or unfolded state of the chain units...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089391/dielectric-constant-of-ionic-solutions-combined-effects-of-correlations-and-excluded-volume
#4
Ram M Adar, Tomer Markovich, Amir Levy, Henri Orland, David Andelman
The dielectric constant of ionic solutions is known to reduce with increasing ionic concentrations. However, the origin of this effect has not been thoroughly explored. In this paper, we study two such possible sources: long-range Coulombic correlations and solvent excluded-volume. Correlations originate from fluctuations of the electrostatic potential beyond the mean-field Poisson-Boltzmann theory, evaluated by employing a field-theoretical loop expansion of the free energy. The solvent excluded-volume, on the other hand, stems from the finite ion size, accounted for via a lattice-gas model...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089390/effective-landau-theory-of-ferronematics
#5
Grigorii Zarubin, Markus Bier, S Dietrich
An effective Landau-like description of ferronematics, i.e., suspensions of magnetic colloidal particles in a nematic liquid crystal (NLC), is developed in terms of the corresponding magnetization and nematic director fields. The study is based on a microscopic model and on classical density functional theory. Ferronematics are susceptible to weak magnetic fields and they can exhibit a ferromagnetic phase, which has been predicted several decades ago and has recently been found experimentally. Within the proposed effective Landau theory of ferronematics, one has quantitative access, e...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089389/atomic-versus-molecular-auger-decay-in-ch-2-cl-2-and-cd-2-cl-2-molecules
#6
A C F Santos, D N Vasconcelos, M A MacDonald, M M Sant'Anna, B N C Tenório, A B Rocha, V Morcelle, N Appathurai, L Zuin
Autoionization spectra of CH2 Cl2 and CD2 Cl2 molecules after Cl 2p excitation are studied. The two molecular and atomic Auger transitions are examined and assigned. The contribution of atomic Auger transitions is lower in the deuterated molecule. In addition, to support the presence of the ultrafast dissociation mechanism in the dichloromethane molecule, a series of high-level ab initio quantum mechanical calculations were performed at multiconfigurational self-consistent field (MCSCF) and multireference configuration interaction (MRCI) levels of theory...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089388/connectedness-percolation-of-hard-convex-polygonal-rods-and-platelets
#7
Tara Drwenski, René van Roij, Paul van der Schoot
The properties of polymer composites with nanofiller particles change drastically above a critical filler density known as the percolation threshold. Real nanofillers, such as graphene flakes and cellulose nanocrystals, are not idealized disks and rods but are often modeled as such. Here we investigate the effect of the shape of the particle cross section on the geometric percolation threshold. Using connectedness percolation theory and the second-virial approximation, we analytically calculate the percolation threshold of hard convex particles in terms of three single-particle measures...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089387/substrate-induced-shifts-and-screening-in-the-fluorescence-spectra-of-supramolecular-adsorbed-organic-monolayers
#8
James Kerfoot, Vladimir V Korolkov, Anton S Nizovtsev, Ryan Jones, Takashi Taniguchi, Kenji Watanabe, Igor Lesanovsky, Beatriz Olmos, Nicholas A Besley, Elena Besley, Peter H Beton
We have investigated the influence of the substrate on the fluorescence of adsorbed organic molecules. Monolayer films of perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI), a supramolecular network formed from PTCDI and melamine, and perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride have been deposited on hexagonal boron nitride (hBN). The principal peaks in the fluorescence spectra of these films were red-shifted by up to 0.37 eV relative to published measurements for molecules in helium droplets...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089386/local-environment-of-organic-dyes-in-an-ionic-liquid-water-mixture-fcs-and-md-simulation
#9
Somen Nandi, Sridip Parui, Biman Jana, Kankan Bhattacharyya
The composition dependent local environment of three organic dyes in binary mixtures of a room temperature ionic liquid (1-methyl-3-pentylimidazolium bromide, [pmim][Br]) and water is studied by fluorescence correlation spectroscopy (FCS) and molecular dynamics (MD) simulations. We used three dyes-neutral coumarin 480 (C480), anionic coumarin 343 (C343), and highly hydrophobic 4-(dicyanomethylene)-2-methyl-6-(p-dimethyl-aminostyryl)-4H-pyran (DCM)-to probe different environments in the binary mixtures. The heterogeneity of the [pmim][Br]-water mixture leads to multiple values (i...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089385/dynamic-nuclear-polarization-of-carbonyl-and-methyl-13-c-spins-of-acetate-using-4-oxo-tempo-free-radical
#10
Christopher Parish, Peter Niedbalski, Andhika Kiswandhi, Lloyd Lumata
Hyperpolarization of 13 C-enriched biomolecules via dissolution dynamic nuclear polarization (DNP) has enabled real-time metabolic imaging of a variety of diseases with superb specificity and sensitivity. The source of the unprecedented liquid-state nuclear magnetic resonance spectroscopic or imaging signal enhancements of >10 000-fold is the microwave-driven DNP process that occurs at a relatively high magnetic field and cryogenic temperature. Herein, we have methodically investigated the relative efficiencies of 13 C DNP of single or double 13 C-labeled sodium acetate with or without 2 H-enrichment of the methyl group and using a 4-oxo-TEMPO free radical as the polarizing agent at 3...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089384/neutron-scattering-studies-on-short-and-long-range-layer-structures-and-related-dynamics-in-imidazolium-based-ionic-liquids
#11
Fumiya Nemoto, Maiko Kofu, Michihiro Nagao, Kazuki Ohishi, Shin-Ichi Takata, Jun-Ichi Suzuki, Takeshi Yamada, Kaoru Shibata, Takeshi Ueki, Yuzo Kitazawa, Masayoshi Watanabe, Osamu Yamamuro
Alkyl-methyl-imidazolium ionic liquids CnmimX (n: alkyl-carbon number, X: anion) have short-range layer structures consisting of ionic and neutral (alkylchain) domains. To investigate the temperature dependences of the interlayer, interionic group, and inter-alkylchain correlations, we have measured the neutron diffraction (ND) of C16mimPF6 , C9.5mimPF6 , and C8mimPF6 in the temperature region from 4 K to 470 K. The quasielastic neutron scattering (QENS) of C16mimPF6 was also measured to study the dynamics of each correlation...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089383/how-much-different-are-thermochemical-properties-of-enantiomers-and-their-racemates-thermochemical-properties-of-enantiopure-and-racemate-of-methyl-and-butyl-lactates
#12
Sergey P Verevkin, Vladimir N Emel'yanenko, Andrey A Pimerzin, Andrei V Yermalayeu
This work is a contribution to the molecular understanding of the thermodynamic properties of the chiral compounds. A comprehensive thermochemical study of the liquid enantiopure and racemate pairs of optically active alkyl lactates has been performed. Vapor pressures of DL-(±)-, L-(-)-methyl-, and DL-(±)-, L-(-)-n-butyl esters of lactic acid were measured by the transpiration method. The liquid phase standard molar enthalpies of formation of these esters were measured by using the high-precision combustion calorimetry...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089382/correlation-anisotropy-and-stiffness-of-dna-molecules-confined-in-nanochannels
#13
Tomáš Bleha, Peter Cifra
The anisotropy of orientational correlations in DNA molecules confined in cylindrical channels is explored by Monte Carlo simulations using a coarse-grained model of double-stranded (ds) DNA. We find that the correlation function ⟨C(s)⟩⊥ in the transverse (confined) dimension exhibits a region of negative values in the whole range of channel sizes. Such a clear-cut sign of the opposite orientation of chain segments represents a microscopic validation of the Odijk deflection mechanism in narrow channels...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089381/relaxation-of-long-lived-modes-in-nmr-of-deuterated-methyl-groups
#14
Konstantin L Ivanov, Thomas Kress, Mathieu Baudin, David Guarin, Daniel Abergel, Geoffrey Bodenhausen, Dennis Kurzbach
Long-lived imbalances of spin state populations can circumvent fast quadrupolar relaxation by reducing effective longitudinal relaxation rates by about an order of magnitude. This opens new avenues for the study of dynamic processes in deuterated molecules. Here we present an analysis of the relaxation properties of deuterated methyl groups CD3 . The number of coupled equations that describe cross-relaxation between the 27 symmetry-adapted spin states of a D3 system can be reduced to only 2 non-trivial "lumped modes" by (i) taking the sums of the populations of all states that equilibrate rapidly within each irreducible representation of the symmetry group, and (ii) by combining populations that have similar relaxation rates although they belong to different irreducible representations...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089380/mean-field-density-functional-theory-of-a-nanoconfined-classical-three-dimensional-heisenberg-fluid-ii-the-interplay-between-molecular-packing-and-orientational-order
#15
Stefanie M Wandrei, Roland Roth, Martin Schoen
As in Paper I of this series of papers [S. M. Cattes et al., J. Chem. Phys. 144, 194704 (2016)], we study a Heisenberg fluid confined to a nanoscopic slit pore with smooth walls. The pore walls can either energetically discriminate specific orientations of the molecules next to them or are indifferent to molecular orientations. Unlike in Paper I, we employ a version of classical density functional theory that allows us to explicitly account for the stratification of the fluid (i.e., the formation of molecular layers) as a consequence of the symmetry-breaking presence of the pore walls...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089379/exotic-electronic-structures-of-sm-x-ce-3-x-o-y-x-0-3-y-2-4-clusters-and-the-effect-of-high-neutral-density-of-low-lying-states-on-photodetachment-transition-intensities
#16
Josey E Topolski, Jared O Kafader, Vicmarie Marrero-Colon, Srinivasan S Iyengar, Hrant P Hratchian, Caroline Chick Jarrold
Lanthanide (Ln) oxide clusters have complex electronic structures arising from the partially occupied Ln 4f subshell. New anion photoelectron (PE) spectra of Smx Ce3-x Oy - (x = 0-3; y = 2-4) along with supporting results of density functional theory (DFT) calculations suggest interesting x and y-dependent Sm 4f subshell occupancy with implications for Sm-doped ionic conductivity of ceria, as well as the overall electronic structure of the heterometallic oxides. Specifically, the Sm centers in the heterometallic species have higher 4f subshell occupancy than the homonuclear Sm3 Oy - /Sm3 Oy clusters...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089378/a-simple-closure-procedure-for-the-study-of-velocity-autocorrelation-functions-in-fluids-as-a-bridge-between-different-theoretical-approaches
#17
V V Ignatyuk, I M Mryglod, T Bryk
Velocity autocorrelation functions (VAFs) of the fluids are studied on short- and long-time scales within a unified approach. This approach is based on an effective summation of the infinite continued fraction at a reasonable assumption about convergence of relaxation times of the high order memory functions, which have a purely kinetic origin. The VAFs obtained within our method are compared with computer simulation data for the liquid Ne at different densities and the results, which follow from the Markovian approximation for the highest order kinetic kernels...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089377/shaped-incoherent-light-for-control-of-kinetics-optimization-of-up-conversion-hues-in-phosphors
#18
François O Laforge, Matthew S Kirschner, Herschel A Rabitz
We propose a method for interactively controlling multi-species atomic and molecular systems with incoherent light. The technique is referred to as shaped incoherent light for control (SILC), which entails dynamically tailoring the spectrum of a broadband incoherent source to control atomic and molecular scale kinetics. Optimal SILC light patterns can be discovered with adaptive learning techniques where the system's observed response is fed back to the control for adjustment aiming to improve the objective...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089376/crystal-nucleation-rates-in-glass-forming-molecular-liquids-d-sorbitol-d-arabitol-d-xylitol-and-glycerol
#19
Chengbin Huang, Zhenxuan Chen, Yue Gui, Chenyang Shi, Geoff G Z Zhang, Lian Yu
The rate of crystal nucleation has been measured in four glass-forming molecular liquids: D-sorbitol, D-arabitol, D-xylitol, and glycerol. These polyalcohols have similar rates of crystal growth when compared at the same temperature relative to Tg (the glass transition temperature), peaking near 1.4 Tg , while the nucleation rates J are vastly different. In D-sorbitol and D-arabitol, J reaches a maximum of ∼108 m-3 s-1 near 1.1 Tg , whereas J < 10-2 m-3 s-1 in D-xylitol and <1 m-3 s-1 in glycerol based on no nucleation in large samples after long waits...
August 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/30089375/density-functional-approximations-for-orbital-energies-and-total-energies-of-molecules-and-solids
#20
Evert Jan Baerends
The relation of Kohn-Sham (KS) orbital energies to ionization energies and electron affinities is different in molecules and solids. In molecules, the local density approximation (LDA) and generalized gradient approximations (GGA) approximate the exact ionization energy (I) and affinity (A) rather well with self-consistently calculated (total energy based) ILDFA and ALDFA , respectively. The highest occupied molecular orbital (HOMO) energy and lowest unoccupied molecular orbital (LUMO) energy, however, differ significantly (by typically 4-6 eV) from these quantities, ϵH LDFA (mol)>-I(mol)≈-ILDFA (mol), ϵL LDFA (mol)<-A(mol)≈-ALDFA (mol)...
August 7, 2018: Journal of Chemical Physics
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