JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

21 May 2013

Volume 138, Issue 19 (partial)

Issue Cover Spotlight Figure

J. Chem. Phys. 138, 195101 (2013); http://dx.doi.org/10.1063/1.4803507 (11 pages)

Mu-Jie Huang, Raymond Kapral, Alexander S. Mikhailov, and Hsuan-Yi Chen
Enlarge Image | Read More
Page 1 of 2 Pages Next Page | Jump to Page
back to top
RSS Feeds
FREE

Communication: Pressure fluctuations in isotropic solids and fluids

J. P. Wittmer, H. Xu, P. Polińska, F. Weysser, and J. Baschnagel

J. Chem. Phys. 138, 191101 (2013); http://dx.doi.org/10.1063/1.4807305 (3 pages)

Online Publication Date: 15 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Comparing isotropic solids and fluids at either imposed volume or pressure, we investigate various correlations of the instantaneous pressure and its ideal and excess contributions. Focusing on the compression modulus K, it is emphasized that the stress fluctuation representation of the elastic moduli may be obtained directly (without a microscopic displacement field) by comparing the stress fluctuations in conjugated ensembles. This is made manifest by computing the Rowlinson stress fluctuation expression Krow of the compression modulus for NPT-ensembles. It is shown theoretically and numerically that Krow|P = Pid(2 − Pid/K) with Pid being the ideal pressure contribution.
Show PACS
46.25.Cc Theoretical studies
62.10.+s Mechanical properties of liquids
02.60.-x Numerical approximation and analysis
FREE

Communication: State-to-state photodissociation study by the two-color VUV-VUV laser pump-probe time-slice velocity-map-imaging-photoion method

Hong Gao, Yu Song, William M. Jackson, and C. Y. Ng

J. Chem. Phys. 138, 191102 (2013); http://dx.doi.org/10.1063/1.4807302 (4 pages)

Online Publication Date: 16 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We demonstrate that combining two independently tunable vacuum ultraviolet (VUV) lasers and the time-slice velocity-map-imaging-photoion (VMI-PI) method allows the rovibronically state-selected photodissociation study of CO in the VUV region along with the state-selective detection of product C(3P0,1,2) using the VUV-UV (1+1′) resonance-enhanced photoionization and the VUV Rydberg autoionization methods. Both tunable VUV lasers are generated based on the two-photon resonance-enhanced four-wave mixing scheme using a pulsed rare gas jet as the nonlinear medium. The observed fine-structure distributions of product C(3PJ), J = 0, 1, and 2, are found to depend on the CO rovibronic state populated by VUV photoexcitation. The branching ratios for C(3P0) + O(3PJ): C(3P0) + O(1D2), C(3P1) + O(3PJ): C(3P1) + O(1D2), and C(3P2) + O(3PJ): C(3P2) + O(1D2), which were determined based on the time-slice VMI-PI measurements of C+ ions formed by J-state selective photoionization sampling of C(3P0,1,2), also reveal strong dependences on the spin-orbit state of C(3P0,1,2). By combining the measured branching ratios and fine-structure distributions of C(3P0,1,2), we have determined the correlated distributions of C(3P0,1,2) accompanying the formation of O(1D2) and O(3PJ) produced in the VUV photodissociation of CO. The success of this demonstration experiment shows that the VUV photodissociation pump-VUV photoionization probe method is promising for state-to-state photodissociation studies of many small molecules, which are relevant to planetary atmospheres as well as fundamental understanding of photodissociation dynamics.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Pw Fine and hyperfine structure
33.20.Ni Vacuum ultraviolet spectra
33.80.Be Level crossing and optical pumping
33.80.Eh Autoionization, photoionization, and photodetachment
back to top
RSS Feeds
back to top Theoretical Methods and Algorithms

Non-linear eigensolver-based alternative to traditional SCF methods

B. Gavin and E. Polizzi

J. Chem. Phys. 138, 194101 (2013); http://dx.doi.org/10.1063/1.4804419 (8 pages)

Online Publication Date: 15 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The self-consistent procedure in electronic structure calculations is revisited using a highly efficient and robust algorithm for solving the non-linear eigenvector problem, i.e., H({ψ})ψ = Eψ. This new scheme is derived from a generalization of the FEAST eigenvalue algorithm to account for the non-linearity of the Hamiltonian with the occupied eigenvectors. Using a series of numerical examples and the density functional theory-Kohn/Sham model, it will be shown that our approach can outperform the traditional SCF mixing-scheme techniques by providing a higher converge rate, convergence to the correct solution regardless of the choice of the initial guess, and a significant reduction of the eigenvalue solve time in simulations.
Show PACS
31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory

Doubly electron-attached and doubly ionized equation-of-motion coupled-cluster methods with 4-particle–2-hole and 4-hole–2-particle excitations and their active-space extensions

Jun Shen and Piotr Piecuch

J. Chem. Phys. 138, 194102 (2013); http://dx.doi.org/10.1063/1.4803883 (16 pages)

Online Publication Date: 16 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The full and active-space doubly electron-attached (DEA) and doubly ionized (DIP) equation-of-motion coupled-cluster (EOMCC) methods with up to 4-particle–2-hole (4p-2h) and 4-hole–2-particle (4h-2p) excitations are developed. By examining bond breaking in F2 and low-lying singlet and triplet states in the methylene, (HFH)−, and trimethylenemethane biradicals, we demonstrate that the DEA- and DIP-EOMCC methods with an active-space treatment of 4p-2h and 4h-2p excitations reproduce the results of the analogous full calculations at the small fraction of the computer effort, while improving the DEA/DIP-EOMCC theories truncated at 3p-1h/3h-1p excitations.
Show PACS
34.80.Ht Dissociation and dissociative attachment
31.15.bw Coupled-cluster theory
33.15.Fm Bond strengths, dissociation energies
31.15.vj Electron correlation calculations for atoms and ions: excited states

Potential energy curves via double electron-attachment calculations: Dissociation of alkali metal dimers

Monika Musiał, Katarzyna Kowalska-Szojda, Dmitry I. Lyakh, and Rodney J. Bartlett

J. Chem. Phys. 138, 194103 (2013); http://dx.doi.org/10.1063/1.4804164 (8 pages)

Online Publication Date: 16 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The recently developed method [M. Musiał, J. Chem. Phys. 136, 134111 (2012)10.1063/1.3700438] to study double electron attached states has been applied to the description of the ground and excited state potential energy curves of the alkali metal dimers. The method is based on the multireference coupled cluster scheme formulated within the Fock space formalism for the (2,0) sector. Due to the use of the efficient intermediate Hamiltonian formulation, the approach is free from the intruder states problem. The description of the neutral alkali metal dimers is accomplished via attaching two electrons to the corresponding doubly ionized system. This way is particularly advantageous when a closed shell molecule dissociates into open shell subunits while its doubly positive cation generates the closed shell fragments. In the current work, we generate the potential energy curves for the ground and multiple excited states of the Li2 and Na2 molecules. In all cases the potential energy curves are smooth for the entire range of interatomic distances (from the equilibrium point to the dissociation limit). Based on the calculated potential energy curves, we are able to compute spectroscopic parameters of the systems studied.
Show PACS
34.80.Ht Dissociation and dissociative attachment
34.80.Lx Recombination, attachment, and positronium formation
31.15.bw Coupled-cluster theory
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states

Uncertainty quantification in MD simulations of concentration driven ionic flow through a silica nanopore. I. Sensitivity to physical parameters of the pore

F. Rizzi, R. E. Jones, B. J. Debusschere, and O. M. Knio

J. Chem. Phys. 138, 194104 (2013); http://dx.doi.org/10.1063/1.4804666 (19 pages)

Online Publication Date: 17 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this article, uncertainty quantification is applied to molecular dynamics (MD) simulations of concentration driven ionic flow through a silica nanopore. We consider a silica pore model connecting two reservoirs containing a solution of sodium (Na+) and chloride (Cl−) ions in water. An ad hoc concentration control algorithm is developed to simulate a concentration driven counter flow of ions through the pore, with the ionic flux being the main observable extracted from the MD system. We explore the sensitivity of the system to two physical parameters of the pore, namely, the pore diameter and the gating charge. First we conduct a quantitative analysis of the impact of the pore diameter on the ionic flux, and interpret the results in terms of the interplay between size effects and ion mobility. Second, we analyze the effect of gating charge by treating the charge density over the pore surface as an uncertain parameter in a forward propagation study. Polynomial chaos expansions and Bayesian inference are exploited to isolate the effect of intrinsic noise and quantify the impact of parametric uncertainty on the MD predictions. We highlight the challenges arising from the heterogeneous nature of the system, given the several components involved, and from the substantial effect of the intrinsic thermal noise.
Show PACS
47.56.+r Flows through porous media
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.52.+j Chaos in fluid dynamics
47.11.Mn Molecular dynamics methods
02.70.Ns Molecular dynamics and particle methods
02.50.Tt Inference methods

Uncertainty quantification in MD simulations of concentration driven ionic flow through a silica nanopore. II. Uncertain potential parameters

F. Rizzi, R. E. Jones, B. J. Debusschere, and O. M. Knio

J. Chem. Phys. 138, 194105 (2013); http://dx.doi.org/10.1063/1.4804669 (16 pages)

Online Publication Date: 17 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This article extends the uncertainty quantification analysis introduced in Paper I for molecular dynamics (MD) simulations of concentration driven ionic flow through a silica nanopore. Attention is now focused on characterizing, for a fixed pore diameter of D = 21 Å, the sensitivity of the system to the Lennard-Jones energy parameters, ɛNa+ and ɛCl−, defining the depth of the potential well for the two ions Na+ and Cl−, respectively. A forward propagation analysis is applied to map the uncertainty in these parameters to the MD predictions of the ionic fluxes. Polynomial chaos expansions and Bayesian inference are exploited to isolate the effect of the intrinsic noise, stemming from thermal fluctuations of the atoms, and properly quantify the impact of parametric uncertainty on the target MD predictions. A Bayes factor analysis is then used to determine the most suitable regression model to represent the MD noisy data. The study shows that the response surface of the Na+ conductance can be effectively inferred despite the substantial noise level, whereas the noise partially hides the underlying trend in the Cl− conductance data over the studied range. Finally, the dependence of the conductances on the uncertain potential parameters is analyzed in terms of correlations with key bulk transport coefficients, namely, viscosity and collective diffusivities, computed using Green-Kubo time correlations.
Show PACS
47.56.+r Flows through porous media
66.20.Cy Theory and modeling of viscosity and rheological properties, including computer simulation
47.52.+j Chaos in fluid dynamics
05.20.Jj Statistical mechanics of classical fluids
back to top Atoms, Molecules, and Clusters

The structures of neutral transition metal doped silicon clusters, SinX (n = 6−9; X = V, Mn)

Pieterjan Claes, Vu Thi Ngan, Marko Haertelt, Jonathan T. Lyon, André Fielicke, Minh Tho Nguyen, Peter Lievens, and Ewald Janssens

J. Chem. Phys. 138, 194301 (2013); http://dx.doi.org/10.1063/1.4803871 (7 pages)

Online Publication Date: 15 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a combined experimental and theoretical investigation of small neutral vanadium and manganese doped silicon clusters SinX (n = 6−9, X = V, Mn). These species are studied by infrared multiple photon dissociation and mass spectrometry. Structural identification is achieved by comparison of the experimental data with computed infrared spectra of low-lying isomers using density functional theory at the B3P86/6-311+G(d) level. The assigned structures of the neutral vanadium and manganese doped silicon clusters are compared with their cationic counterparts. In general, the neutral and cationic SinV0,+ and SinMn0,+ clusters have similar structures, although the position of the capping atoms depends for certain sizes on the charge state. The influence of the charge state on the electronic properties of the clusters is also investigated by analysis of the density of states, the shapes of the molecular orbitals, and NBO charge analysis of the dopant atom.
Show PACS
36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Cg Electronic and magnetic properties of clusters
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.20.Ea Infrared spectra
33.15.Ta Mass spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation

Water nanodroplets: Predictions of five model potentials

Sergey Kazachenko and Ajit J. Thakkar

J. Chem. Phys. 138, 194302 (2013); http://dx.doi.org/10.1063/1.4804399 (10 pages)

Online Publication Date: 15 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Putative global minima for five intermolecular potential energy models are reported for water clusters (H2O)n with n ⩽ 55. The models studied include three empirical, pairwise-additive potential energy surfaces, TIP4P, TIP4P-Ew, and TIP4P/2005, which use fixed point charges and rigid monomers. The other two, TTM2.1-F and AMOEBA, are polarizable, include non-additive inductive effects, have flexible monomers, and were parametrized, at least partially, using ab initio data. The n = 51 cluster has the same structure and is exceptionally stable for all five potentials. A structured inner core can be seen in cage clusters with n > 37. Periplanar rings, branched rings, and coils are among the structural motifs of the inner core.
Show PACS
36.40.Mr Spectroscopy and geometrical structure of clusters
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.50.-x Potential energy surfaces
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

The ethyl radical in superfluid helium nanodroplets: Rovibrational spectroscopy and ab initio computations

Paul L. Raston, Jay Agarwal, Justin M. Turney, Henry F. Schaefer, III, and Gary E. Douberly

J. Chem. Phys. 138, 194303 (2013); http://dx.doi.org/10.1063/1.4804435 (13 pages)

Online Publication Date: 15 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The ethyl radical has been isolated and spectroscopically characterized in 4He nanodroplets. The band origins of the five CH stretch fundamentals are shifted by < 2 cm−1 from those reported for the gas phase species [S. Davis, D. Uy, and D. J. Nesbitt, J. Chem. Phys. 112, 1823 (2000)10.1063/1.480746; T. Häber, A. C. Blair, D. J. Nesbitt, and M. D. Schuder, J. Chem. Phys. 124, 054316 (2006)10.1063/1.2140740]. The symmetric CH2 stretching band (v1) is rotationally resolved, revealing nuclear spin statistical weights predicted by G12 permutation-inversion group theory. A permanent electric dipole moment of 0.28 (2) D is obtained via the Stark spectrum of the v1 band. The four other CH stretch fundamental bands are significantly broadened in He droplets and lack rotational fine structure. This broadening is attributed to symmetry dependent vibration-to-vibration relaxation facilitated by the He droplet environment. In addition to the five fundamentals, three a1′ overtone/combination bands are observed, and each of these have resolved rotational substructure. These are assigned to the 2v12, v4 + v6, and 2v6 bands through comparisons to anharmonic frequency computations at the CCSD(T)/cc-pVTZ level of theory.
Show PACS
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
31.15.xh Group-theoretical methods
31.30.jp Electron electric dipole moment
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis

A new ab initio based global HOOH(13A″) potential energy surface for the O(3P) + H2O(X1A1) ↔ OH(X2Π) + OH(X2Π) reaction

Jun Li and Hua Guo

J. Chem. Phys. 138, 194304 (2013); http://dx.doi.org/10.1063/1.4804418 (10 pages)

Online Publication Date: 16 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An accurate global potential energy surface is developed for the title reaction by fitting more than 36 000 of ab initio points at the CCSD(T)/AVTZ level using the permutation invariant polynomial method. The canonical rate constants for both the forward and reverse directions of the title reaction are determined on the new potential energy surface and the agreement with experiment is satisfactory. In addition, the dynamics of the forward reaction is investigated with the quasi-classical trajectory method. It is found that this direct abstraction reaction has a backward bias in its product angular distribution, consistent with a direct rebound mechanism. The OH product newly formed by the reaction exhibits a bimodal rotational state distribution, due apparently to secondary collisions with the slowly recoiling spectator OH product.
Show PACS
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Fd Collision theories; trajectory models
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies

Direct-dynamics VTST study of hydrogen or deuterium abstraction and C–C bond formation or dissociation in the reactions of CH3 + CH4, CH3 + CD4, CH3D + CD3, CH3CH3 + H, and CH3CD3 + D

Shapour Ramazani

J. Chem. Phys. 138, 194305 (2013); http://dx.doi.org/10.1063/1.4803862 (10 pages)

Online Publication Date: 20 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Direct-dynamics variational transition-state theory calculations are studied at the MPWB1K/6-311++G(d,p) level for the four parts of reactions. The first part is hydrogen or deuterium abstraction in the reactions of CH3 + CH4, CH3 + CD4, and CH3D + CH3. The second part involves C–C bond formation in these reactions. The third one is the reactions of CH3CH3 + H and CH3CD3 + D to form of H2, HD, and D2. The last one is the dissociation of C–C bonds in the last group of reactions. The ground-state vibrational adiabatic potential is plotted for all channels. We have carried out direct-dynamics calculations of the rate constants, including multidimensional tunneling in the temperature range T = 200–2200 K. The results of CVT/μOMT rate constants were in good agreement with the experimental data which were available for some reactions. Small-curvature tunneling and Large-curvature tunneling with the LCG4 version were used to include the quantum effects in calculation of the rate constants. To try to find the region of formation and dissociation of bounds we have also reported the variations of harmonic vibrational frequencies along the reaction path. The thermally averaged transmission probability (P(E)exp (−ΔE/RT)) and representative tunneling energy at 298 K are reported for the reactions in which tunneling is important. We have calculated kinetic isotope effect which shows tunneling and vibrational contributions are noticeable to determine the rate constant. Nonlinear least-squares fitting is used to calculate rate constant expressions in the temperature range 200–2200 K. These expressions revealed that pre-exponential factor includes two parts; the first part is a constant number which is important at low temperatures while the second part is temperature dependent which is significant at high temperatures.
Show PACS
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Hf Product distribution
82.20.Tr Kinetic isotope effects including muonium

Low-energy electron collisions with thiophene

R. F. da Costa, M. T. do N. Varella, M. A. P. Lima, and M. H. F. Bettega

J. Chem. Phys. 138, 194306 (2013); http://dx.doi.org/10.1063/1.4805107 (6 pages)

Online Publication Date: 20 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report on elastic integral, momentum transfer, and differential cross sections for collisions of low-energy electrons with thiophene molecules. The scattering calculations presented here used the Schwinger multichannel method and were carried out in the static-exchange and static-exchange plus polarization approximations for energies ranging from 0.5 eV to 6 eV. We found shape resonances related to the formation of two long-lived π* anion states. These resonant structures are centered at the energies of 1.00 eV (2.85 eV) and 2.82 eV (5.00 eV) in the static-exchange plus polarization (static-exchange) approximation and belong to the B1 and A2 symmetries of the C2v point group, respectively. Our results also suggest the existence of a σ* shape resonance in the B2 symmetry with a strong d-wave character, located at around 2.78 eV (5.50 eV) as obtained in the static-exchange plus polarization (static-exchange) calculation. It is worth to mention that the results obtained at the static-exchange plus polarization level of approximation for the two π* resonances are in good agreement with the electron transmission spectroscopy results of 1.15 eV and 2.63 eV measured by Modelli and Burrow [J. Phys. Chem. A 108, 5721 (2004)10.1021/jp048759a]. The existence of the σ* shape resonance is in agreement with the observations of Dezarnaud-Dandiney et al. [J. Phys. B 31, L497 (1998)10.1088/0953-4075/31/11/004] based on the electron transmission spectra of dimethyl(poly)sulphides. A comparison among the resonances of thiophene with those of pyrrole and furan is also performed and, altogether, the resonance spectra obtained for these molecules point out that electron attachment to π* molecular orbitals is a general feature displayed by these five-membered heterocyclic compounds.
Show PACS
34.80.Bm Elastic scattering
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
34.80.Lx Recombination, attachment, and positronium formation
back to top Liquids, Glasses, and Crystals

Structure of kaolinite and influence of stacking faults: Reconciling theory and experiment using inelastic neutron scattering analysis

Claire E. White, Gordon J. Kearley, John L. Provis, and Daniel P. Riley

J. Chem. Phys. 138, 194501 (2013); http://dx.doi.org/10.1063/1.4804306 (7 pages)

Online Publication Date: 15 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The structure of kaolinite at the atomic level, including the effect of stacking faults, is investigated using inelastic neutron scattering (INS) spectroscopy and density functional theory (DFT) calculations. The vibrational dynamics of the standard crystal structure of kaolinite, calculated using DFT (VASP) with normal mode analysis, gives good agreement with the experimental INS data except for distinct discrepancies, especially for the low frequency modes (200 – 400 cm−1). By generating several types of stacking faults (shifts in the a,b plane for one kaolinite layer relative to the adjacent layer), it is seen that these low frequency modes are affected, specifically through the emergence of longer hydrogen bonds (O–H⋯O) in one of the models corresponding to a stacking fault of −0.3151a − 0.3151b. The small residual disagreement between observed and calculated INS is assigned to quantum effects (which are not taken into account in the DFT calculations), in the form of translational tunneling of the proton in the hydrogen bonds, which lead to a softening of the low frequency modes. DFT-based molecular dynamics simulations show that anharmonicity does not play an important role in the structural dynamics of kaolinite.
Show PACS
61.72.Nn Stacking faults and other planar or extended defects
82.30.Rs Hydrogen bonding, hydrophilic effects
61.50.Lt Crystal binding; cohesive energy
63.20.dh Fitted theory

Intermolecular interactions and the thermodynamic properties of supercritical fluids

Tesfaye M. Yigzawe and Richard J. Sadus

J. Chem. Phys. 138, 194502 (2013); http://dx.doi.org/10.1063/1.4803855 (11 pages)

Online Publication Date: 16 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The role of different contributions to intermolecular interactions on the thermodynamic properties of supercritical fluids is investigated. Molecular dynamics simulation results are reported for the energy, pressure, thermal pressure coefficient, thermal expansion coefficient, isothermal and adiabatic compressibilities, isobaric and isochoric heat capacities, Joule-Thomson coefficient, and speed of sound of fluids interacting via both the Lennard-Jones and Weeks-Chandler-Andersen potentials. These properties were obtained for a wide range of temperatures, pressures, and densities. For each thermodynamic property, an excess value is determined to distinguish between attraction and repulsion. It is found that the contributions of intermolecular interactions have varying effects depending on the thermodynamic property. The maxima exhibited by the isochoric and isobaric heat capacities, isothermal compressibilities, and thermal expansion coefficient are attributed to interactions in the Lennard-Jones well. Repulsion is required to obtain physically realistic speeds of sound and both repulsion and attraction are necessary to observe a Joule-Thomson inversion curve. Significantly, both maxima and minima are observed for the isobaric and isochoric heat capacities of the supercritical Lennard-Jones fluid. It is postulated that the loci of these maxima and minima converge to a common point via the same power law relationship as the phase coexistence curve with an exponent of β = 0.32. This provides an explanation for the terminal isobaric heat capacity maximum in supercritical fluids.
Show PACS
61.43.Bn Structural modeling: serial-addition models, computer simulation
64.70.-p Specific phase transitions
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
65.40.De Thermal expansion; thermomechanical effects
65.40.Ba Heat capacity
back to top Surfaces, Interfaces, and Materials

Elementary steps of the catalytic NOx reduction with NH3: Cluster studies on adsorbate diffusion and dehydrogenation at vanadium oxide substrate

M. Gruber and K. Hermann

J. Chem. Phys. 138, 194701 (2013); http://dx.doi.org/10.1063/1.4804160 (11 pages)

Online Publication Date: 15 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We discuss the details of important steps of the selective catalytic reduction (SCR) of NOx at model V2O5(010) substrate. First, diffusion processes at the substrate surface are considered where hydrogen and ammonium, NH4, are used as examples. Hydrogen diffusion, a prerequisite for water formation involving substrate oxygen, is described by diffusion paths between adjacent surface oxygen sites. Corresponding energy barriers are determined mainly by the flexibility and the amount of distortion of the oxygen atoms which participate in the O–H–O bridge formation at the transition state. Further, diffusion of sub-surface oxygen to fill surface oxygen vacancies of the V2O5(010) substrate has been considered and results in reactive surface sites which have not been discussed so far. NH4 diffusion at the V2O5(010) surface can be described as a combined tumbling and rotation process characterized by quite low diffusion barriers which make the adsorbate rather mobile. Finally, hydrogenation and dehydrogenation of different NHx species at the V2O5(010) substrate surface are studied where special emphasis is given to the influence of surface reduction simulated locally by oxygen vacancies. The results confirm experimental findings of the presence of both NH2 and NH4 species after ammonia adsorption at the V2O5(010) surface.
Show PACS
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.43.Mn Adsorption kinetics
68.47.Gh Oxide surfaces

Density functional theory study of the organic functionalization of hydrogenated silicene

Pamela Rubio-Pereda and Noboru Takeuchi

J. Chem. Phys. 138, 194702 (2013); http://dx.doi.org/10.1063/1.4804545 (7 pages)

Online Publication Date: 16 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Silicene, the silicon analogous of graphene, is a newly synthesized two-dimensional nanomaterial, with unique features and promising potential applications. In this paper we present density functional theory calculations of the organic functionalization of hydrogenated silicene with acetylene, ethylene, and styrene. The results are compared with previous works of the adsorption on H-Si[111]. For styrene, binding energies for the intermediate and final states as well as the energy barrier for hydrogen abstraction are rather similar for the two systems. On the other hand, results for acetylene and ethylene are surprisingly different in H-silicene: the abstraction barrier is much smaller in H-silicene than in H-Si[111]. These differences can be understood by the different electrostatic potentials due to the presence of the H atoms at the bottom of the silicene bilayer that allows the delocalization of the spin density at the reaction intermediate state.
Show PACS
68.43.Mn Adsorption kinetics
71.15.Nc Total energy and cohesive energy calculations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

KAg11(VO4)4 as a candidate p-type transparent conducting oxide

Jino Im, Giancarlo Trimarchi, Haowei Peng, Arthur J. Freeman, Veerle Cloet, Adam Raw, and Kenneth R. Poeppelmeier

J. Chem. Phys. 138, 194703 (2013); http://dx.doi.org/10.1063/1.4804556 (7 pages)

Online Publication Date: 16 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
For a material to be a good p-type transparent conducting oxide (TCO), it must simultaneously satisfy several design principles regarding its bulk and defect phase thermochemistry, its optical absorption spectrum, and its electric transport properties. Recently, we predicted Ag3VO4 to be p-type but with low conductivity and an optical band gap not large enough for transparency. To improve on the transport and optical properties of Ag3VO4, we searched an extended material space including quaternary compounds based on Ag, V, O, and an additional atom for a new candidate p-type TCO. From this set of quaternary materials, we selected KAg11(VO4)4, a known oxide with a crystal structure related to that of Ag3VO4. Notably, one could expect a possible enhancement of the concentration of hole producing Ag-vacancy defects in KAg11(VO4)4 due to its different local geometries of Ag atoms (2- and 3-fold coordinated) with respect to the 4-fold coordinated Ag atoms in Ag3VO4. By performing first-principles calculations, we found that KAg11(VO4)4 is an intrinsic p-type conductor and can be synthesized under conditions similar to those predicted for the synthesis of Ag3VO4. However, we predict that the intrinsic hole content in KAg11(VO4)4 is similar to that in Ag3VO4 even though KAg11(VO4)4 contains 2- and 3-fold coordinated Ag, hole producing sites with a lower defect formation energy than the 4-fold coordinated one. Our calculation demonstrates that the advantage from lower coordination number of the Ag atom in KAg11(VO4)4 can be offset by the change in the range of Ag chemical potential in which synthesis is allowed due to the oxide phases that Ag forms with K and that energetically compete with KAg11(VO4)4.
Show PACS
71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.jd Vacancies
61.66.Fn Inorganic compounds
71.55.Ht Other nonmetals
81.10.Dn Growth from solutions

Functionalization of carbon nanotubes with –CHn, –NHn fragments, –COOH and –OH groups

Karolina Z. Milowska and Jacek A. Majewski

J. Chem. Phys. 138, 194704 (2013); http://dx.doi.org/10.1063/1.4804652 (14 pages)

Online Publication Date: 16 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present results of extensive theoretical studies concerning stability, morphology, and band structure of single wall carbon nanotubes (CNTs) covalently functionalized by –CHn (for n = 2,3,4), –NHn (for n = 1,2,3,4), –COOH, and –OH groups. These studies are based on ab initio calculations in the framework of the density functional theory. For functionalized systems, we determine the dependence of the binding energies on the concentration of the adsorbed molecules, critical densities of adsorbed molecules, global and local changes in the morphology, and electronic structure paying particular attention to the functionalization induced changes of the band gaps. These studies reveal physical mechanisms that determine stability and electronic structure of functionalized systems and also provide valuable theoretical predictions relevant for application. In particular, we observe that functionalization of CNTs causes generally their elongation and locally sp2 to sp3 rehybridization in the neighborhood of chemisorbed molecules. For adsorbants making particularly strong covalent bonds with the CNTs, such as the –CH2 fragments, we observe formation of the characteristic pentagon/heptagon (5/7) defects. In systems functionalized with the –CH2, –NH4, and –OH groups, we determine critical density of molecules that could be covalently bound to the lateral surface of CNTs. Our studies show that functionalization of CNTs can be utilized for band gap engineering. Functionalization of CNTs can also lead to changes in their metallic/semiconductor character. In semiconducting CNTs, functionalizing molecules such as –CH3, –NH2, –OH, –COOH, and both –OH and –COOH, introduce “impurity” bands in the band gap of pristine CNTs. In the case of –CH3, –NH2 molecules, the induced band gaps are typically smaller than in the pure CNT and depend strongly on the concentration of adsorbants. However, functionalization of semiconducting CNTs with hydroxyl groups leads to the metallization of CNTs. On the other hand, the functionalization of semi-metallic (9,0) CNT with –CH2 molecules causes the increase of the band gap and induces semi-metall to semiconductor transition.
Show PACS
73.22.-f Electronic structure of nanoscale materials and related systems
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
68.43.Mn Adsorption kinetics
71.15.Nc Total energy and cohesive energy calculations
61.46.Fg Nanotubes

Electronic structure and quantum dynamics of photoinitiated dissociation of O2 on rutile TiO2 nanocluster

Pratik P. Dholabhai and Hua-Gen Yu

J. Chem. Phys. 138, 194705 (2013); http://dx.doi.org/10.1063/1.4805000 (12 pages)

Online Publication Date: 16 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The adsorption and photoinitiated dissociation of molecular oxygen on reduced rutile TiO2 nanocluster have been studied using a hybrid density functional theory (DFT)/time-dependent DFT approach and a time-dependent wavepacket dynamics method. Results show that the most favorable state for O2 at the bridging row O-vacancy site of TiO2 is O22− with an orientation parallel to the surface. We find that its dissociation in the electronic ground state involves a spin forbidden intersystem crossing, and therefore has a large barrier along the reaction pathway. However, time-dependent wavepacket calculations reveal that the photoinitiated O2 dissociation on TiO2 is very fast via a direct mechanism on the excited states. The lifetime of excited O2 molecules is predicted to be about 266 fs. Non-adiabatic effects among the singlet electronic states are found to play an important role in the O2 dissociation whereas the spin-orbit effect is negligible. In addition, adsorption of two O2 molecules at an O-vacancy site shows that the second O2 molecule can stabilize the system by about 0.22 eV.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Qv Stability and fragmentation of clusters
36.40.Wa Charged clusters
68.43.Mn Adsorption kinetics
31.15.E- Density-functional theory
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.80.Be Level crossing and optical pumping

On the properties of binary rutile MO2 compounds, M = Ir, Ru, Sn, and Ti: A DFT study

Gerard Novell-Leruth, Giuliano Carchini, and Núria López

J. Chem. Phys. 138, 194706 (2013); http://dx.doi.org/10.1063/1.4803854 (10 pages)

Online Publication Date: 20 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have studied the properties of bulk and different surfaces of rutile oxides, IrO2, RuO2, SnO2, and TiO2, and their binary compounds by means of density functional theory. As mixtures are employed in many applications, we have investigated the solubility, segregation, and overlayer formation of one of these oxides on a second metal from the series, as these aspects are critical for the chemical and electrochemical performances. Our results show that the bulk solubility is possible for several combinations. The electronic structure analysis indicates the activation of Ir states in IrxTi1−xO2 mixtures when compared to the parent IrO2 compound or the reduction in the band gap of TiO2 when Sn impurities are present. Segregation and oxygen-induced segregation of the second metal for the most common surfaces show a great extent of possibilities ranging from strong segregation to antisegregation, which depends on the oxygen ambient. The interaction of guest rutile overlayers on hosts is favourable and a wide range of growth properties (from multilayer formation to tridimensional particles) can be observed. Finally, a careful comparison with experimental information is presented, and for those cases where no data is available, the computed database can be used as a guideline by experimentalists.
Show PACS
68.35.Dv Composition, segregation; defects and impurities
64.75.Bc Solubility
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

The striped phases of ethylthiolate monolayers on the Au(111) surface: A scanning tunneling microscopy study

Fangsen Li, Lin Tang, Oleksandr Voznyy, Jianzhi Gao, and Quanmin Guo

J. Chem. Phys. 138, 194707 (2013); http://dx.doi.org/10.1063/1.4806969 (7 pages)

Online Publication Date: 20 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Striped phases of ethylthiolate monolayers, corresponding to surface coverage in between 0.2 ML and 0.27 ML, were studied using high-resolution scanning tunneling microscopy. Striped phases consist of rows of Au-adatom-diethythiolate (AAD) aligned along the [11math] direction. In the perpendicular [1math0] direction, the AAD rows adjust their spacing according to the surface coverage. A (5√3 × √3)-R30° striped phase with 0.27 ML thiolate and a (6√3 × √3)-R30° striped phase with 0.23 ML thiolate, both with long-range order, are found. A localized (5 × √3)-rect. phase is also found as a minority phase embedded in the 5√3 × √3)-R30° phase. This (5 × √3)-rect. phase can be constructed using di-Au-adatom-tri-thiolate species.
Show PACS
68.43.Mn Adsorption kinetics
68.43.Fg Adsorbate structure (binding sites, geometry)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
back to top Polymers and Soft Matter

A density functional theory of chiral block copolymer melts

Shih-Hao Wang, Toshihiro Kawakatsu, Peilong Chen, and Chun-Yi David Lu

J. Chem. Phys. 138, 194901 (2013); http://dx.doi.org/10.1063/1.4802963 (9 pages)

Online Publication Date: 15 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A density functional theory is developed for the diblock copolymer melt, where one block contains the segment orientation dependent chiral interaction. In addition to the standard (scalar) pair interaction between the two types of monomers, the chiral block has the additional pairwise interaction, which is linear in the tangent vectors of the segments. We construct a density functional, which contains both the scalar density field and the vector chain alignment field. The quadratic part of the density functional comes from the mean field theory of the microscopic model, whereas the fourth order terms are introduced phenomenologically in the spatially local form. From the stability analysis of this model, we find that the additional chiral interaction shifts the order-disorder transition, which is consistent with the behavior of experimental system. Further numerical calculation reveals a new metastable chiral helical cylinder structure, which is similar to the one found experimentally. Another similar metastable structure but with zigzag modulation is also observed. As the helical and zigzag structures disappear when the chiral interaction is switched off, we understand that the chiral effect is the driving force for the formation of these exotic metastable structures.
Show PACS
61.25.hk Polymer melts and blends
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.10.Li Excited states and pairing interactions in model systems
64.60.Cn Order-disorder transformations

Numerical study of a slip-link model for polymer melts and nanocomposites

Diego Del Biondo, Elian M. Masnada, Samy Merabia, Marc Couty, and Jean-Louis Barrat

J. Chem. Phys. 138, 194902 (2013); http://dx.doi.org/10.1063/1.4799263 (13 pages)

Online Publication Date: 15 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a numerical study of the slip link model introduced by Likhtman for describing the dynamics of dense polymer melts. After reviewing the technical aspects associated with the implementation of the model, we extend previous work in several directions. The dependence of the relaxation modulus with the slip link density and the slip link stiffness is reported. Then the nonlinear rheological properties of the model, for a particular set of parameters, are explored. Finally, we introduce excluded volume interactions in a mean field such as manner in order to describe inhomogeneous systems, and we apply this description to a simple nanocomposite model. With this extension, the slip link model appears as a simple and generic model of a polymer melt, that can be used as an alternative to molecular dynamics for coarse grained simulations of complex polymeric systems.
Show PACS
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
83.80.Sg Polymer melts
62.25.-g Mechanical properties of nanoscale systems
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.20.F- Deformation and plasticity

Liquid-crystal mediated nanoparticle interactions and gel formation

Jonathan K. Whitmer, Abhijeet A. Joshi, Tyler F. Roberts, and Juan J. de Pablo

J. Chem. Phys. 138, 194903 (2013); http://dx.doi.org/10.1063/1.4802774 (10 pages)

Online Publication Date: 17 May 2013

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Colloidal particles embedded within nematic liquid crystals exhibit strong anisotropic interactions arising from preferential orientation of nematogens near the particle surface. Such interactions are conducive to forming branched, gel-like aggregates. Anchoring effects also induce interactions between colloids dispersed in the isotropic liquid phase, through the interactions of the pre-nematic wetting layers. Here we utilize computer simulation using coarse-grained mesogens to perform a molecular-level calculation of the potential of mean force between two embedded nanoparticles as a function of anchoring for a set of solvent conditions straddling the isotropic–nematic transition. We observe that strong, nontrivial interactions can be induced between particles dispersed in mesogenic solvent, and explore how such interactions might be utilized to induce a gel state in the isotropic and nematic phases.
Show PACS
82.70.Gg Gels and sols
64.70.M- Transitions in liquid crystals
61.20.Ja Computer simulation of liquid structure
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.70.Dd Colloids
Page 1 of 2 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close