bluuebunny/crossref_metadata_2025 huggingface dataset:
Deceleration of relative streaming between proton components among nonlinear low‐frequency Alfvén waves
Authors: Kaghashvili Edisher K. , Vasquez Bernard J. , Zank Gary P. , Hollweg Joseph V.
Published: November 2004

Proton distributions in fast solar winds often have a beam component with a differential streaming speed near the local Alfvén speed. The Alfvén speed and differential streaming speed decrease with increasing distance from the Sun. Thus the beam decelerates, especially within 1 AU where β (which is ratio of plasma to magnetic pressure) can be significantly smaller than unity. We present 2 1/2‐dimensional hybrid numerical simulation results of the evolution of particle proton components streaming relative to each other for moderate relative beam densities (up to 50%) for initially isotropic distributions with mostly equal beam and main proton temperatures and small plasma β(=0.2). Electrons are treated as a fluid. We consider cases without and with initial nonlinear low‐frequency (nearly dispersionless) shear Alfvén waves propagating in the direction of the beam. Without initial waves, a strong linear beam instability can occur for streaming speeds above the Alfvén speed generating oblique proton‐proton cyclotron waves through both cyclotron and Landau resonances. The initial beam speed can decelerate and saturate at speeds below the Alfvén speed. When nonlinear Alfvén waves are included in simulations, we find that the deceleration rates are enhanced. Deceleration is especially strong for initial super‐Alfvénic speeds where we interpret the results with initial waves to be due to a wave amplification of the linear beam instability.
Atmospheric front over the East China Sea studied by multisensor satellite and in situ data
Authors: Ivanov Andrei Y. , Alpers Werner , Litovchenko Konstantin T. , He Ming‐Xia , Feng Qian , Fang Mingqiang , Yan Xiao‐Hai
Published: November 2004

A frontal feature visible on a synthetic aperture radar (SAR) image acquired by the Radarsat satellite over the East China Sea on 19 November 2000 is analyzed in conjunction with data acquired by Quikscat, TOPEX/Poseidon, Tropical Rain Measurement Mission (TRMM), Defense Meteorological Satellite Program (DMSP), and National Oceanic and Atmospheric Administration (NOAA) satellites, and with data obtained from ship measurements. Although this frontal feature is located close to the Kuroshio front, it is demonstrated that it is not a sea surface manifestation of an oceanic front, but rather of an atmospheric front extending over 800 km from an area of the Pacific Ocean northeast of Taiwan to the southern coast of Korea. It is a cold front moving in the southeast direction with a speed of approximately 45–50 km/hour and associated with a 40‐km‐wide rainband trailing the front. The Radarsat image, which has a resolution of 50 m, reveals fine‐scale structures of the atmospheric front, in particular small‐scale convective rain cells embedded in the front. Conclusion is drawn that accurate interpretation of frontal features in SAR images requires use of additional meteorological and remote sensing data and information.
Multiresolution quantum chemistry: Basic theory and initial applications
Authors: Harrison Robert J. , Fann George I. , Yanai Takeshi , Gan Zhengting , Beylkin Gregory
Published: November 2004

We describe a multiresolution solver for the all-electron local density approximation Kohn-Sham equations for general polyatomic molecules. The resulting solutions are obtained to a user-specified precision and the computational cost of applying all operators scales linearly with the number of parameters. The construction and use of separated forms for operators (here, the Green’s functions for the Poisson and bound-state Helmholtz equations) enable practical computation in three and higher dimensions. Initial applications include the alkali-earth atoms down to strontium and the water and benzene molecules.
Variationally optimized basis orbitals for biological molecules
Authors: Ozaki T. , Kino H.
Published: November 2004

Numerical atomic basis orbitals are variationally optimized for biological molecules such as proteins, polysaccharides, and deoxyribonucleic acid within a density functional theory. Based on a statistical treatment of results of a fully variational optimization of basis orbitals ( full optimized basis orbitals) for 43 biological model molecules, simple sets of preoptimized basis orbitals classified under the local chemical environment (simple preoptimized basis orbitals) are constructed for hydrogen, carbon, nitrogen, oxygen, phosphorous, and sulfur atoms, each of which contains double valence plus polarization basis function. For a wide variety of molecules we show that the simple preoptimized orbitals provide well convergent energy and physical quantities comparable to those calculated by the full optimized orbitals, which demonstrates that the simple preoptimized orbitals possess substantial transferability for biological molecules.
Electronic structure, vibrational stability, and predicted infrared-Raman spectra of the As20, As@Ni12, and As@Ni12@As20 clusters
Authors: Baruah Tunna , Zope Rajendra R. , Richardson Steven L. , Pederson Mark R.
Published: November 2004

Recently an inorganic fullerine-like [As@Ni12@As20]3− onion with near-perfect icosahedral symmetry in the crystalline phase was reported [M. J. Moses, J. C. Fettinger, and B. W. Eichhorn, Science 300, 778 (2003)]. This paper presents a detailed computational study in the framework of density functional theory on various aspects of this molecule. The electronic structure of the As@Ni12@As20 is investigated in its neutral as well as −3 charged state together with its subunits As20 and As@Ni12 by the all electron linear combination of Gaussian-type orbitals method. The bonding is studied by examining the integrated charge within atomic sphere, the electron localization function, changes in the electron density distribution, and from vibrational modes. We find that strong covalent As-As bonds seen in isolated As20 become weaker in the As@Ni12@As20 and strong covalent As-Ni bonds are formed. The structural stability of all four clusters is examined by analyzing the energetics and by calculating the vibrational frequencies. Further, the infrared and Raman spectra is predicted for both the neutral and charged As@Ni12@As20 clusters. Finally, the energy barrier for removal of a single arsenic atom is calculated for the neutral As@Ni12@As20 cluster.
Photochemistry of ethylene: A multireference configuration interaction investigation of the excited-state energy surfaces
Authors: Barbatti M. , Paier J. , Lischka H.
Published: November 2004

Multireference configuration interaction with singles and doubles (MR-CISD) calculations have been performed for the optimization of conical intersections and stationary points on the ethylene excited-state energy surfaces using recently developed methods for the computation of analytic gradients and nonadiabatic coupling terms. Basis set dependence and the effect of various choices of reference spaces for the MR-CISD calculations have been investigated. The crossing seam between the S0 and S1 states has been explored in detail. This seam connects all conical intersections presently known for ethylene. Major emphasis has been laid on the hydrogen-migration path. Starting in the V state of twisted-orthogonal ethylene, a barrierless path to ethylidene was found. The feasibility of ethylidene formation will be important for the explanation of the relative yield of cis and trans H2 elimination.
A realistic kinetic Monte Carlo simulation of the faceting of a Pt(110) surface under reaction conditions
Authors: Monine M. I. , Pismen L. M. , Imbihl R.
Published: November 2004

The faceting process on Pt(110) is studied with the help of a kinetic Monte Carlo model taking into account realistic Pt–Pt, Pt–CO, and Pt–O interactions. The activation energies of the allowed atomic steps are estimated using available computational and experimental data. The model well reproduces the region in the parameter space where faceting occurs. Under kinetic instability conditions, the simulated faceted pattern forms a periodic hill and valley structure with a lateral periodicity of ∼140–170 Å, which is comparable with experimental data. The simulations reproduce the development of faceting on a realistic time scale.
Molecular dynamics and density functional theory simulations of matrix deposition. II. Absolute site structure assignment for porphyrin in xenon
Authors: Kyrychenko Alexander , Gorski Alexander , Waluk Jacek
Published: November 2004

Molecular dynamics calculations reveal that the main trapping site for porphyrin embedded in a xenon matrix corresponds to a hexagonal cavity formed after removal of seven host atoms. Tautomerization involving two inner hydrogen atoms leads to two trans forms that interact differently with the matrix cage. Therefore, both electronic and infrared spectra are split into doublets. Comparison of the experimentally observed splitting patterns with the results of density functional theory calculations that explicitly include the nearest xenon atoms allows assigning each spectral feature to one of two different configurations of the chromophore inside the xenon cavity. The main factor responsible for the splittings is a distortion of the molecular skeleton from a squarelike towards rectangular geometry.
Intermolecular potential energy surface and spectra of He–HCl with generalization to other rare gas–hydrogen halide complexes
Authors: Murdachaew Garold , Szalewicz Krzysztof , Jiang Hao , Bačić Zlatko
Published: November 2004

A two-dimensional (rigid monomer) intermolecular potential energy surface (PES) of the He–HCl complex has been obtained from ab initio calculations utilizing the symmetry-adapted perturbation theory (SAPT) and an spdfg basis set including midbond functions. The bond length in HCl was chosen to be equal to the expectation value in the ground vibrational state of isolated HCl. The rigid-monomer potential should be a very good approximation to the complete (three-dimensional) potential for H–Cl distances corresponding to the lowest vibrational levels of the monomer since the He–HCl interaction energy was found to be only weakly dependent on the HCl bond length in this region, at least as compared to systems such as Ar–HF. The calculated points were fitted using an analytic function with ab initio computed asymptotic coefficients. As expected, the complex is loosely bound, with the dispersion energy providing the majority of the attraction. Our SAPT PES agrees with the semiempirical PES of Willey et al. [J. Chem. Phys. 96, 898 (1992)], in finding that, atypically for rare gas–hydrogen halide complexes including the lighter halide atoms, the global minimum is on the Cl side (with intermonomer separation 3.35 Å and depth of 32.8 cm−1), rather than on the H side, where there is only a local minimum (3.85 Å, 30.8 cm−1). The ordering of the minima was confirmed by single-point calculations in larger basis sets and complete basis set extrapolations, and also using higher levels of theory. We show that the opposite findings in the recent calculations of Zhang and Shi [J. Mol. Struct: THEOCHEM 589, 89 (2002)] are due to the lack of midbond functions in their basis set. Despite the closeness in depth of the two linear minima, the existence of a relatively high barrier between them invalidates the assumption of isotropy, a feature of some literature potentials. The trends concerning the locations of minima within the family of rare gas–hydrogen halide complexes are rationalized in terms of the physical components of the intermolecular forces and related to monomer properties. The accuracy of the SAPT PES was tested by performing calculations of rovibrational levels. The transition frequencies obtained were found to be in excellent agreement (to within 0.02 cm−1) with the measurements of Lovejoy and Nesbitt [J. Chem. Phys. 93, 5387 (1990)]. The SAPT PES predicts a dissociation energy for the complex of 7.74 cm−1 which is probably more accurate than the experimental value of 10.1±1.2 cm−1. Our analysis of the ground-state rovibrational wave function shows that the He–HCl configuration is favored over the He–ClH configuration despite the ordering of minima. This is due to the greater volume of the well in the former case. We have also determined positions and widths of three low-lying resonance states through scattering calculations. These predictions are expected to be more accurate than values derived from experiment.
First principles determination of the bound levels of HeLi−
Authors: Backlund Ben , Shih Alex , Gellene Gregory I.
Published: November 2004

An analytical potential energy curve is developed from high quality ab initio calculations for the He+Li− interaction. The HeLi− electrostatic complex is found to have an Re of 18.5 bohrs and a De of 0.974 cm−1. Numerical solution of the rovibrational Schrödinger equation with this potential indicates two bound levels, (v,J)=(0,0) and (0,1), for all naturally occurring isotopologs (i.e., He4Li−7, He4Li−6, He3Li−7, and He3Li−6). For the common isotopolog, He4Li−7, a D0 of 0.207 cm−1 and an R0 of 26.5 bohrs is determined.
Action spectroscopy and temperature diagnostics of H3+ by chemical probing
Authors: Mikosch J. , Kreckel H. , Wester R. , Plašil R. , Glosı́k J. , Gerlich D. , Schwalm D. , Wolf A.
Published: November 2004

Infrared absorption spectroscopy of few hundred H3+ ions trapped in a 22-pole ion trap is presented using chemical probing as a sensitive detection technique down to the single ion level. By exciting selected overtone transitions of the (v1=0,v2l=31)←(0,00) vibrational band using an external cavity diode laser an accurate diagnostics measurement of the effective translational and rotational temperatures of the trapped ions was performed. The absolute accuracy of the measured transition frequencies was improved by a factor of four compared to previous plasma spectroscopy measurements using velocity modulation [Ventrudo et al., J. Chem. Phys. 100, 6263 (1994)]. The observed buffer gas cooling conditions in the ion trap indicate how to cool trapped H3+ ions into the lowest ortho and para rotational states. Future experiments will utilize such an internally cold ion ensemble for state-selected dissociative recombination experiments at the heavy ion storage ring Test Storage Ring (TSR).
Comment on “New phase for one-component hard spheres” [J. Chem. Phys. 120, 11686 (2004)]
Authors: Blaak Ronald , Löwen Hartmut , Barrat Jean-Louis
Published: November 2004

We argue that the claim of a third, thermodynamical stable phase in monodisperse hard sphere system is based on a wrong interpretation of the simulation data. Configurations, made available by the authors, are used to demonstrate that it is an artificially, by periodic boundaries stabilized phase with fcc signature and some defects.
Density functional investigations of the properties and thermochemistry of UFn and UCln (n=1,…,6)
Authors: Batista Enrique R. , Martin Richard L. , Hay P. Jeffrey
Published: November 2004

The structural properties and thermochemistry of the UFn and UCln (n=1,…,6) molecules have been investigated using hybrid density functional theory and a small-core (60 electrons) relativistic effective core potential for the uranium atom. For the first time Bond dissociation energies for this whole series are computed and shown to be in good agreement with experiment. The geometry and electronic structure of each molecule was characterized.
Diffusion-limited transport of I3− through nanoporous TiO2-polymer gel networks
Authors: Dürr M. , Kron G. , Rau U. , Werner J. H. , Yasuda A. , Nelles G.
Published: November 2004

Tri-iodide transport in a polymer gel electrolyte embedded in nanoporous TiO2 networks and its diffusion limits are investigated by means of current-voltage (I–V) characteristics of simple Pt-gel-Pt sandwich devices with a thin porous TiO2 layer sintered directly onto one of the Pt electrodes. At voltages between 0.2 and 0.7 V, the I–V curves of such devices show the typical plateau of diffusion-limited redox reactions, in this case I−/I3−, at the platinum electrodes. From the dependence of the limiting current density on layer thickness, the diffusion constants Dbulk and Dp,eff of tri-iodide in the bulk polymer gel and through a polymer gel penetrated TiO2 network, respectively, have been found to be Dbulk=3.2(±0.2)×10−6 cm2/s and Dp,eff=1.5(±0.1)×10−6 cm2/s. Temperature-dependent measurements show diffusion in the gel to be activated by about 0.16 eV. The results are discussed in comparison to diffusion in liquid electrolytes as well as with respect to the implications for dye-sensitized solar cell devices.
Corrugation energy for octane on Cu(111)
Authors: Bruch L. W.
Published: November 2004

The energy barrier for sliding of octane on Cu(111) is estimated from an experimental datum for the Brillouin-zone-center gap for translation of a monolayer solid of the octane.
A canonical averaging in the second-order quantized Hamilton dynamics
Authors: Heatwole Eric , Prezhdo Oleg V.
Published: November 2004

Quantized Hamilton dynamics (QHD) is a simple and elegant extension of classical Hamilton dynamics that accurately includes zero-point energy, tunneling, dephasing, and other quantum effects. Formulated as a hierarchy of approximations to exact quantum dynamics in the Heisenberg formulation, QHD has been used to study evolution of observables subject to a single initial condition. In present, we develop a practical solution for generating canonical ensembles in the second-order QHD for position and momentum operators, which can be mapped onto classical phase space in doubled dimensionality and which in certain limits is equivalent to thawed Gaussian. We define a thermal distribution in the space of the QHD-2 variables and show that the standard β=1/kT relationship becomes β′=2/kT in the high temperature limit due to an overcounting of states in the extended phase space, and a more complicated function at low temperatures. The QHD thermal distribution is used to compute total energy, kinetic energy, heat capacity, and other canonical averages for a series of quartic potentials, showing good agreement with the quantum results.
Temperature-dependent micellar structures in poly(styrene-b-isoprene) diblock copolymer solutions near the critical micelle temperature
Authors: Bang Joona , Viswanathan Karthik , Lodge Timothy P. , Park Moon Jeong , Char Kookheon
Published: November 2004

The temperature dependence of the micelle structures formed by poly(styrene-b-isoprene) (SI) diblock copolymers in the selective solvents diethyl phthalate (DEP) and tetradecane (C14), which are selective for the PS and PI blocks, respectively, have been investigated by small angle neutron scattering (SANS). Two nearly symmetric SI diblock copolymers, one with a perdeuterated PS block and the other with a perdeuterated PI block, were examined in both DEP and C14. The SANS scattering length density of the solvent was matched closely to either the core or the corona block. The resulting core and corona contrast data were fitted with a detailed model developed by Pedersen and co-workers. The fits provide quantitative information on micellar characteristics such as aggregation number, core size, overall size, solvent fraction in the core, and corona thickness. As temperature increases, the solvent selectivity decreases, leading to substantial solvent swelling of the core and a decrease in the aggregation number and core size. Both core and corona chains are able to relax their conformations near the critical micelle temperature due to a decrease in the interfacial tension, even though the corona chains are always under good solvent conditions.
Thermal conductivity of solid argon at high pressure and high temperature: A molecular dynamics study
Authors: Tretiakov Konstantin V. , Scandolo Sandro
Published: November 2004

The thermal conductivity of solid argon at high-pressure (up to 50 GPa) and high-temperature (up to 2000 K) has been calculated by equilibrium molecular dynamics simulations using the Green–Kubo formalism and an exponential-6 interatomic potential. A simple empirical expression is given for its pressure and temperature dependence. The results are compared with predictions based on kinetic theory. The relative change of the thermal conductivity λ with density ρ is found to be consistent with a ∂ ln λ/∂ ln ρ slope of approximately 6 in a wide range of pressures and temperatures, in good agreement with predictions based on kinetic theory.
C–Cl bond fission dynamics and angular momentum recoupling in the 235 nm photodissociation of allyl chloride
Authors: Liu Yi , Butler Laurie J.
Published: November 2004

The photodissociation dynamics of allyl chloride at 235 nm producing atomic Cl(2PJ;J=1/2,3/2) fragments is investigated using a two-dimensional photofragment velocity ion imaging technique. Detection of the Cl(2P1/2) and Cl(2P3/2) products by [2+1] resonance enhanced multiphoton ionization shows that primary C–Cl bond fission of allyl chloride generates 66.8% Cl(2P3/2) and 33.2% Cl(2P1/2). The Cl(2P3/2) fragments evidenced a bimodal translational energy distribution with a relative weight of low kinetic energy Cl(2P3/2)/high kinetic energy Cl(2P3/2) of 0.097/0.903. The minor dissociation channel for C–Cl bond fission, producing low kinetic energy chlorine atoms, formed only chlorine atoms in the Cl(2P3/2) spin–orbit state. The dominant C–Cl bond fission channel, attributed to an electronic predissociation that results in high kinetic energy Cl atoms, produced both Cl(2P1/2) and Cl(2P3/2) atomic fragments. The relative branching for this dissociation channel is Cl(2P1/2)/[Cl(2P1/2)+Cl(2P3/2)]=35.5%. The average fraction of available energy imparted into product recoil for the high kinetic energy products was found to be 59%, in qualitative agreement with that predicted by a rigid radical impulsive model. Both the spin–orbit ground and excited chlorine atom angular distributions were close to isotropic. We compare the observed Cl(2P1/2)/[Cl(2P1/2)+Cl(2P3/2)] ratio produced in the electronic predissociation channel of allyl chloride with a prior study of the chlorine atom spin–orbit states produced from HCl photodissociation, concluding that angular momentum recoupling in the exit channel at long interatomic distance determines the chlorine atom spin–orbit branching.
The curvature of the conical intersection seam: An approximate second-order analysis
Authors: Paterson Martin J. , Bearpark Michael J. , Robb Michael A. , Blancafort Lluı́s
Published: November 2004

We present a method for analyzing the curvature (second derivatives) of the conical intersection hyperline at an optimized critical point. Our method uses the projected Hessians of the degenerate states after elimination of the two branching space coordinates, and is equivalent to a frequency calculation on a single Born–Oppenheimer potential-energy surface. Based on the projected Hessians, we develop an equation for the energy as a function of a set of curvilinear coordinates where the degeneracy is preserved to second order (i.e., the conical intersection hyperline). The curvature of the potential-energy surface in these coordinates is the curvature of the conical intersection hyperline itself, and thus determines whether one has a minimum or saddle point on the hyperline. The equation used to classify optimized conical intersection points depends in a simple way on the first- and second-order degeneracy splittings calculated at these points. As an example, for fulvene, we show that the two optimized conical intersection points of C2v symmetry are saddle points on the intersection hyperline. Accordingly, there are further intersection points of lower energy, and one of C2 symmetry—presented here for the first time—is found to be the global minimum in the intersection space.
Activation of tubulin assembly into microtubules upon a series of repeated femtosecond laser impulses
Authors: Tulub Alexander A. , Stefanov Vasily E.
Published: November 2004

Tubulin, a globular protein, mostly distributed in nature in the dimeric α, β form, can polymerize in vivo and in vitro into microtubules—longitudinal dynamic assemblies, involved in numerous cellular functions, including cell division and signaling. Tubulin polymerization starts upon binding Mg2+ with the tubulin guanosine triphosphate (GTP) site. In the current study we show that a series of repeated femtosecond laser impulses activate the same site without adding Mg2+. GTP site activation (without GTP no polymerization occurs) produces hydrated electrons (they are detected by the UV spectra), which are trapped in the shell of biological water, surrounding the tubulin. These electrons generate an additional, nonlinear by nature, polarization effect, responsible for the second harmonic generation at λ=365 nm (the first harmonic is centered at λ=730 nm) and manyfold increase in strength of the initial electric field. The results are supported by model calculations, based on the assumption of positive (negative) feedback, appearing on interaction of charge transfer exciton dipoles with the applied electromagnetic field.
Short chains at solid surfaces: Wetting transition from a density functional approach
Authors: Bryk P. , Sokołowski S.
Published: November 2004

A microscopic density functional theory is used to investigate the adsorption of short chains on attractive solid surfaces. We analyze the structure of the adsorbed fluid and investigate how the wetting transition changes with the change of the chain length and with the relative strength of the fluid-solid interaction. End segments adsorb preferentially in the first adsorbed layer whereas the concentration of the middle segments is enhanced in the second layer. We observe that the wetting temperature rescaled by the bulk critical temperature decreases with an increase of the chain length. For longer chains this temperature reaches a plateau. For the surface critical temperature an inverse effect is observed, i.e., the surface critical temperature increases with the chain length and then attains a plateau. These findings may serve as a quick estimate of the wetting and surface critical temperatures for fluids of longer chain lengths.
On the critical cluster in the two-dimensional Ising model: Computer-assisted exact results
Authors: Shneidman Vitaly A. , Nita Gelu M.
Published: November 2004

For a nearest-neighbor Ising model on a square lattice all cluster configurations with 17 or fewer spins are identified. In neglect of cluster-cluster interactions, critical sizes and barriers to nucleation are obtained as functions of temperature and magnetic field for two alternative definitions of a “critical cluster.”
Methane activation by nickel cluster cations, Nin+ (n=2–16): Reaction mechanisms and thermochemistry of cluster-CHx (x=0–3) complexes
Authors: Liu Fuyi , Zhang Xiao-Guang , Liyanage Rohana , Armentrout P. B.
Published: November 2004

The kinetic energy dependences of the reactions of Nin+ (n=2–16) with CD4 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0–10 eV. The main products are hydride formation NinD+, dehydrogenation to form NinCD2+, and double dehydrogenation yielding NinC+. These primary products decompose at higher energies to form NinCD+, Nin−1D+, Nin−1C+, Nin−1CD+, and Nin−1CD2+. NinCD2+ (n=5–9) and Nin−1CD2+ (n⩾4) are not observed. In general, the efficiencies of the single and double dehydrogenation processes increase with cluster size. All reactions exhibit thresholds, and cross sections for the various primary and secondary reactions are analyzed to yield reaction thresholds from which bond energies for nickel cluster cations to C, CD, CD2, and CD3 are determined. The relative magnitudes of these bond energies are consistent with simple bond order considerations. Bond energies for larger clusters rapidly reach relatively constant values, which are used to estimate the chemisorption energies of the C, CD, CD2, and CD3 molecular fragments to nickel surfaces.
The Huggins band of ozone: A theoretical analysis
Authors: Qu Zheng-Wang , Zhu Hui , Grebenshchikov Sergy Yu. , Schinke Reinhard , Farantos Stavros C.
Published: November 2004

The Huggins band of ozone is investigated by means of dynamics calculations using a new (diabatic) potential energy surface for the 3 1A′(1B2) state. The good overall agreement of the calculated spectrum of vibrational energies and intensities with the experimental spectrum, especially at low to intermediate excitation energies, is considered as evidence that the Huggins band is due to the two Cs potential wells of the B21 state rather than the single C2v well of the 2 1A′(1A1) state. The vibrational assignment of the “cold bands,” based on the nodal structure of wave functions, on the whole supports the most recent experimental assignment [J. Chem. Phys. 115, 9311 (2001)]. The quantum mechanical spectrum is analyzed in terms of classical periodic orbits and the structure of the classical phase space.
Using preconditioned adaptive step size Runge-Kutta methods for solving the time-dependent Schrödinger equation
Authors: Tremblay Jean Christophe , Carrington Tucker
Published: November 2004

If the Hamiltonian is time dependent it is common to solve the time-dependent Schrödinger equation by dividing the propagation interval into slices and using an (e.g., split operator, Chebyshev, Lanczos) approximate matrix exponential within each slice. We show that a preconditioned adaptive step size Runge-Kutta method can be much more efficient. For a chirped laser pulse designed to favor the dissociation of HF the preconditioned adaptive step size Runge-Kutta method is about an order of magnitude more efficient than the time sliced method.
Formation of high density amorphous ice by decompression of ice VII and ice VIII at 135 K
Authors: McBride Carl , Vega Carlos , Sanz Eduardo , Abascal Jose L. F.
Published: November 2004

Monte Carlo computer simulations of ice VII and ice VIII phases have been undertaken using the four-point transferable intermolecular potential model of water. By following thermodynamic paths similar to those used experimentally, ice is decompressed resulting in an amorphous phase. These phases are compared to the high density amorphous phase formed upon compression of ice Ih and are found to have very similar structures. By cooling liquid water along the water/Ih melting line a high density amorphous phase was also generated.
Lower and upper bounds for the absolute free energy by the hypothetical scanning Monte Carlo method: Application to liquid argon and water
Authors: White Ronald P. , Meirovitch Hagai
Published: November 2004

The hypothetical scanning (HS) method is a general approach for calculating the absolute entropy S and free energy F by analyzing Boltzmann samples obtained by Monte Carlo or molecular dynamics techniques. With HS applied to a fluid, each configuration i of the sample is reconstructed by gradually placing the molecules in their positions at i using transition probabilities (TPs). At each step of the process the system is divided into two parts, the already treated molecules (the “past”), which are fixed, and the as yet unspecified (mobile) “future” molecules. Obtaining the TP exactly requires calculating partition functions over all positions of the future molecules in the presence of the frozen past, thus it is customary to invoke various approximations to best represent these quantities. In a recent publication [Proc. Natl. Acad. Sci. USA 101, 9235 (2004)] we developed a version of HS called complete HSMC, where each TP is calculated from an MC simulation involving all of the future molecules (the complete future); the method was applied very successfully to Lennard-Jones systems (liquid argon) and a box of TIP3P water molecules. In its basic implementation the method provides lower and upper bounds for F, where the latter can be evaluated only for relatively small systems. Here we introduce a new expression for an upper bound, which can be evaluated for larger systems. We also propose a new exact expression for F and verify its effectiveness. These free energy functionals lead to significantly improved accuracy (as applied to the liquid systems above) which is comparable to our thermodynamic integration results. We formalize and discuss theoretical aspects of HSMC that have not been addressed in previous studies. Additionally, several functionals are developed and shown to provide the free energy through the analysis of a single configuration.
Damage induced by low-energy electrons in solid films of tetrahydrofuran
Authors: Breton S.-P. , Michaud M. , Jäggle C. , Swiderek P. , Sanche L.
Published: November 2004

We report on the low-energy electron-induced production of aldehydes within thin solid films of tetrahydrofuran (THF) condensed on a solid Kr substrate. The aldehyde fragments, which remain trapped within the bulk of the THF film, are detected in situ via their (n→π*)3,1 and (π→π*)3 electronic transitions and vibrational excitations in the ground state using high-resolution electron-energy-loss spectroscopy. The production of aldehyde is studied as a function of the electron exposure, film thickness, and incident electron energy between 1 and 18.5 eV. The aldehyde production is calibrated in terms of an electron scattering cross section, which is found to be typically 6–7×10−17 cm2 between 11 and 19 eV. Its energy dependence is characterized by a small feature around 3 eV, a strong rise from 6 eV up to a maximum at 12.5 eV, followed by two structures centered around 15 and 18 eV. The aldehyde production is discussed in terms of the formation of electron resonances or transient anion states, which may lead to the fragmentation of the molecule and explain the structures seen in the energy dependence of the measured cross section.
Chemiluminescent reactions of manganese with fluorine: Influence of dynamics on product energy partitioning in vibration and rotation of MnF*(b,c)
Authors: Green Karen M. , Parson John M.
Published: November 2004

Chemiluminescent exit channels of Mn+F2→MnF*+F were investigated using the molecular beam technique in a beam-gas configuration with an array detector. Two uncongested regions, corresponding to MnF transitions c 5Σ+(b)-a 5Σ+(b) and b 5Πi(int)-a 5Σ+(b) were fit for vibrational and rotational populations, which were used to develop a microscopic reaction mechanism for these chemiluminescent exit channels. In both MnF* electronic states, significant vibrational excitation but little rotational excitation was found. Significant vibrational excitation has been attributed to early energy release as Mn loses an electron at long range to the lowest unoccupied molecular orbital on F2. The incipient bond is strengthened as backbonding from the F2− to Mn+ increases the covalent character of the intermediate. Finally, no strict geometric constraints are placed on the exit channel and hence there is no significant repulsive energy release into product rotation. Our proposed mechanism exhibits dynamic control in that the course of the reaction is determined by both geometric factors and dynamic factors.
Relativistic density-functional all-electron calculations of interconfigurational energies of lanthanide atoms
Authors: Ren Chung-Yuan
Published: November 2004

The interconfigurational energies (ICEs) of the lanthanide atoms, including the s ionization energies, the f ionization energy, and the fd transition energy, are studied based on the fully relativistic density-functional theory (RDFT). The exchange-correlation energy functional by the local-spin-density approximation (RLSD), the generalized gradient approximation (RGGA), and the approximation within the framework of the Krieger-Li-Iafrate treatment of the optimized effective potential (ROEP) incorporated by an explicit self-interaction correction term are used to perform the calculation. In addition, results obtained from the simple perturbation with the mass-velocity correction and the Darwin shift are also presented for comparisons. It is found that the ROEP, with the proper description of the long-range behavior of the outermost electron, yields the most best computations for the two s ionizations. For the f ionization potential and the fd transition energy, the RGGA surpasses the RLSD and the ROEP, reflecting the importance of the gradient expansion in dealing with the more localized f or d electron densities. The excellent satisfaction of the Koopmans’ theorem for the two s binding energies is demonstrated within the ROEP framework. As predicted in previous work [C. Y. Ren, H. T. Jeng, and C. S. Hsue, Phys. Rev. B 66, 125105 (2002)], the perturbative ICEs for the first s ionization are almost the same with those by the fully RDFT through the whole lanthanide atoms, with a deviation smaller than 0.1 eV. However, the similarity of calculations by means of the fully RDFT and the standard perturbation method is destroyed in the cases of the f ionization and the fd transition energy.
A density functional study on nitrogen-doped carbon clusters CnN3− (n=1–8)
Authors: Chen Mingdan , Liu Jianwen , Dang Li , Zhang Qianer , Au C. T.
Published: November 2004

Using molecular graphics software, we designed numerous models of CnN3− (n=1–8). Geometry optimization and calculation on vibration frequency were carried out by the B3LYP density functional method. After comparison of structure stability, we found that the structures of ground-state CN3− and C2N3− are bent chains with a nitrogen atom at either end, whereas when n=3–8, the ground-state clusters show three branches, each with a nitrogen atom located at the end. When n=5–8, the longest branch of CnN3− is polyacetylenelike. When n=5 or 7, the longest branch is connected to the central sp2 carbon in a nonlinear manner. The CnN3− (n=1–8) with an even number of carbon atoms are more stable than those with odd numbers, matching the peak pattern observed in laser-induced mass spectra of CnN3−. The trend of such odd/even alternation is explained based on concepts of bonding characteristics, electron affinities, and incremental binding energies.
Globally convergent trust-region methods for self-consistent field electronic structure calculations
Authors: Francisco Juliano B. , Martı́nez José Mario , Martı́nez Leandro
Published: November 2004

As far as more complex systems are being accessible for quantum chemical calculations, the reliability of the algorithms used becomes increasingly important. Trust-region strategies comprise a large family of optimization algorithms that incorporates both robustness and applicability for a great variety of problems. The objective of this work is to provide a basic algorithm and an adequate theoretical framework for the application of globally convergent trust-region methods to electronic structure calculations. Closed shell restricted Hartree–Fock calculations are addressed as finite-dimensional nonlinear programming problems with weighted orthogonality constraints. A Levenberg–Marquardt-like modification of a trust-region algorithm for constrained optimization is developed for solving this problem. It is proved that this algorithm is globally convergent. The subproblems that ensure global convergence are easy-to-compute projections and are dependent only on the structure of the constraints, thus being extendable to other problems. Numerical experiments are presented, which confirm the theoretical predictions. The structure of the algorithm is such that accelerations can be easily associated without affecting the convergence properties.
Study of ab initio molecular data for inelastic and reactive collisions involving the H3+ quasimolecule
Authors: Barragán P. , Errea L. F. , Macı́as A. , Méndez L. , Rabadán I. , Riera A. , Lucas J. M. , Aguilar A.
Published: November 2004

The lowest two ab initio potential energy surfaces (PES), and the corresponding nonadiabatic couplings between them, have been obtained for the H3+ system; the molecular data are compared to those calculated with the diatomic in molecules (DIM) method. The form of the couplings is discussed in terms of the topology of the molecular structure of the triatomic. The method of Baer is employed to generate “diabatic” states and the residual nonadiabatic couplings are calculated. The ab initio results for these are markedly different from the corresponding DIM data, and show the need to consider the third PES.
Hydrodynamics and microphase ordering in block copolymers: Are hydrodynamics required for ordered phases with periodicity in more than one dimension?
Authors: Horsch Mark A. , Zhang Zhenli , Iacovella Christopher R. , Glotzer Sharon C.
Published: November 2004

We use Brownian dynamics (BD), molecular dynamics, and dissipative particle dynamics to study the phase behavior of diblock copolymer melts and to determine if hydrodynamics is required in the formation of phases with greater than one-dimensional periodicity. We present a phase diagram for diblock copolymers predicted by BD and provide a relationship between the inverse dimensionless temperature ε/kBT and the Flory–Huggins χ parameter, allowing for a quantitative comparison between methods and to mean field predictions. Our results concerning phase behavior are in good qualitative agreement with the theoretical predictions of Matsen and Bates [M. W. Matsen and F. S. Bates, Macromolecules 29, 1091 (1996)]; however, fluctuation effects arising from finite polymer lengths substantially alter the phase boundaries. Our results pertaining to the hydrodynamics are in contrast to earlier work by Groot et al. [R. D. Groot, T. J. Madden, and D. J. Tildesley, J. Chem. Phys. 110, 9739 (1999); D. Frenkel and B. Smit, Understanding Molecular Simulation, 2nd ed. (Academic, New York, 2001)]. In particular, we obtain the hexagonal ordered cylinder phase with BD, a method that does not include hydrodynamics.
Crossed beams and theoretical studies of the dynamics of hyperthermal collisions between Ar and ethane
Authors: Brunsvold Amy L. , Garton Donna J. , Minton Timothy K. , Troya Diego , Schatz George C.
Published: November 2004

Crossed molecular beams experiments and classical trajectory calculations have been used to study the dynamics of Ar+ethane collisions at hyperthermal collision energies. Experimental time-of-flight and angular distributions of ethane molecules that scatter into the backward hemisphere (with respect to their original direction in the center-of-mass frame) have been collected. Translational energy distributions, derived from the time-of-flight distributions, reveal that a substantial fraction of the collisions transfer abnormally large amounts of energy to internal excitation of ethane. The flux of the scattered ethane molecules increased only slightly from directly backward scattering to sideways scattering. Theoretical calculations show angular and translational energy distributions which are in reasonable agreement with the experimental results. These calculations have been used to examine the microscopic mechanism for large energy transfer collisions (“supercollisions”). Collinear (“head-on”) or perpendicular (“side-on”) approaches of Ar to the C–C axis of ethane do not promote energy transfer as much as bent approaches, and collisions in which the H atom is “sandwiched” in a bent Ar⋯H–C configuration lead to the largest energy transfer. The sensitivity of collisional energy transfer to the intramolecular potential energy of ethane has also been examined.
Isotropic-nematic transition of hard rods immersed in random sphere matrices
Authors: Schmidt Matthias , Dijkstra Marjolein
Published: November 2004

Using replica density functional theory and Monte Carlo computer simulations we investigate a system of annealed hard spherocylinders adsorbed in a matrix of quenched hard spheres. Theoretical predictions for the partition coefficient, defined as the ratio of density of rods in the matrix and that in a reservoir, agree well with simulation results. Theory predicts the isotropic-nematic transition to remain first order upon increasing sphere packing fraction, and to shift towards lower rod densities. This scenario is consistent with our simulation results that clearly show a jump in the nematic order parameter upon increasing the rod density at constant matrix packing fraction, corresponding to the isotropic-nematic transition, even for sphere matrix packing fractions ≲0.3.
Effect of electron-phonon coupling on the conductance of a one-dimensional molecular wire
Authors: Lakshmi S. , Pati Swapan K.
Published: November 2004

The effect of inelastic scattering, particularly that of the electron-phonon interactions, on the current-voltage characteristics of a one-dimensional tight-binding molecular wire has been investigated. The wire has been modeled using the Su-Schreiffer-Heeger Hamiltonian and we compute the current using the Landauer’s scattering formalism. Our calculations show that the presence of strong electron-lattice coupling in the wire can induce regions of negative differential resistance (NDR) in the I-V curves. The reasons for this can be traced back to the quasidegeneracy in few of the low-energy molecular levels in the presence of electron-phonon coupling and an external applied bias. The molecular levels become highly delocalized at the critical bias at which the NDR is seen, corresponding to the vanishing of the electron-phonon coupling with equal bond lengths.
Bound states of the barium atom by the hyperspherical approach
Authors: Cebim M. A. , De Groote J. J.
Published: November 2004

We present a nonadiabatic hyperspherical calculation of the highly excited and low lying doubly excited states of the barium atom using effective potentials for the two optically active electrons’ interactions. Within the hyperspherical adiabatic approach the investigation of the spectra is performed with potential curves and nonadiabatic couplings of a unique radial variable, which allows clear identification of the states. The convergence of energy is obtained within well established bound limits, and the precision is comparable to accurate configuration interaction calculations. A very good agreement with experimental results is obtained with only few nonadiabatic couplings.
Monitoring structural changes of liquids frozen in nanopores
Authors: Choi C. , Pintar M. M. , Peternelj J. , Krainer A.
Published: November 2004

Less dense packing of molecules in frozen liquids confined to cylindrical glass pores was observed to depend on pore size. This conclusion was derived by monitoring the rotational tunneling of methyl protons, which reside on studied molecules, with nuclear magnetic resonance. For example, the tunneling frequency of dimethyl sulfide and propionic acid at 10 K was observed to be larger in pores than in bulk. This is interpreted as being due to a decrease in the hindering potential. In another type of tunneling spectrum which is due to methyl-methyl interaction, observed in acetyl acetone at 10 K, the splitting decreases as the pores become smaller. It is demonstrated that in both types of materials the shifts of the methyl tunneling splittings in pores are the result of the reduced intermolecular interaction in the pore core region. This in turn indicates that the unit cell size of liquids frozen in nanopores is slightly increased. The increase is largest in smallest pores.
Modeling nonionic aqueous solutions: The acetone-water mixture
Authors: Perera Aurlien , Sokolić Franjo
Published: November 2004

Several combinations of existing classical water and acetone models are studied by molecular dynamic simulations in order to sort out which models can reproduce available experimental data: enthalpies, pressure, densities, diffusion coefficients, and Kirkwood–Buff integrals. It turns out that all these properties, but the last, are rather well reproduced by all models, and with little numerical effort. By contrast, trials to measure by simulations the Kirkwood–Buff integrals lead to very long simulation times, thus revealing unexpected divergent behavior between the different models, such as phase separation, for example, and ultimately leading to a failure of any models combinations to reproduce these properties according to the experimental tendencies. It is argued herein that these deficiencies provide, in fact, an insightful picture of the microscopic structure of the solution, particularly into the relation between the hydrogen-bond network and the concentration fluctuations, as well as the role played by the solute in their spatial organization.