bluuebunny/crossref_metadata_2025 huggingface dataset:
Orientation dependence of fatigue behavior in relaxor ferroelectric–PbTiO3 thin films
Authors: Bornand V. , Trolier-McKinstry S. , Takemura K. , Randall C. A.
Published: July 2002

Pb[Yb 1/2 Nb 1/2 ]O 3 – PbTiO 3  (PYbN-PT)/SrRuO3 (SRO) capacitors with Pt top electrodes were grown by pulsed laser deposition onto (100)pc LaAlO3 (LAO) and (111)c SrTiO3 (STO) substrates (the subscripts pc and c refer here to the pseudocubic and cubic perovskite cells, respectively). Suitable changes in both the substrate orientation and processing conditions allowed the growth of perovskite structured ferroelectric films with various degrees of orientation, from highly 〈001〉pc-oriented PYbN-PT/SRO/LAO to highly 〈111〉pc-oriented PYbN-PT/SRO/STO heterostructures. It was found that fatigue characteristics of such as-grown planar capacitors are strongly dependent on their crystalline orientation. In particular, 〈001〉pc-heteroepitaxial thin films result in fatigue-free capacitors up to 1011 cycles, while 〈111〉pc-oriented heterostructures exhibit a marked degradation of the switchable polarization by ac voltage cycling. These data are consistent with recent findings of fatigue anisotropy in relaxor ferroelectric-PbTiO3 single crystals.
Spin-valve thermal stability: The effect of different antiferromagnets
Authors: Anderson G. W. , Huai Yiming , Pakala Mahendra
Published: July 2002

This investigation focused on how spin-valve thermal stability is related to different antiferromagnetic materials: FeMn, IrMn, NiMn, PtMn, and PtPdMn. Measurements of the spin-valve exchange biasing field versus temperature show the following relationship in blocking temperatures: FeMn<IrMn<PtPdMn<PtMn<NiMn. Looking at the blocking temperature distributions, both FeMn and IrMn show sharp peaks, but at low temperatures (∼110 °C). In the case of the other materials, the distribution peaks at much higher temperature (>250 °C), but are broader. Pinned angle rotation and giant magnetoresistance versus temperature measurements give the same thermal stability hierarchy, as well as providing information about interdiffusion in these spin-valves. For comparison, synthetic antiferromagnet spin-valves (based on IrMn and PtMn) were also measured. The synthetic structures did not show significantly different blocking temperatures or giant magnetoresistance temperature dependence than standard spin-valves. However, blocking temperature distribution and pinned layer rotation measurements showed improved stability for the synthetic structures, which may be attributed to the very thin effective pinned layer which results in high exchange biasing fields in these structures.
The nuclear shielding derivative and spin–spin coupling in nitrogen
Authors: Friedrich Jan O. , Wasylishen Roderick E.
Published: July 2002

The 15N/14N isotope shift on the 15N chemical shielding in a mixture of 15N14N and 15N15N was found to be 0.0601±0.0022 ppm. Using a model developed by Jameson, the nuclear shielding derivative with respect to bond length was calculated from the measured isotope shift, [∂σ(15N)/∂r]e =−910±42 ppm/Å. This value is in excellent agreement with a value obtained from the temperature dependence of the shielding constant in the gas phase (at the zero pressure limit) and with a value determined from recent molecular orbital calculations. From relaxation measurements the scalar spin–spin coupling constant, 1J(14N,15N), in 14N15N was calculated to be 1.8±0.6 Hz which gives a reduced coupling constant, 1K(N,N)=2.0±0.7 (1020)m−2kg s−2 Å−2. The magnitude of the reduced coupling constant is compared to that of other isoelectronic species and molecular orbital calculations.
Efficient recursive computation of molecular integrals over Cartesian Gaussian functions
Authors: Obara S. , Saika A.
Published: July 2002

Recurrence expressions are derived for various types of molecular integrals over Cartesian Gaussian functions by the use of the recurrence formula for three-center overlap integrals. A number of characteristics inherent in the recursive formalism allow an efficient scheme to be developed for molecular integral computations. With respect to electron repulsion integrals and their derivatives, the present scheme with a significant saving of computer time is found superior to other currently available methods. A long innermost loop incorporated in the present scheme facilitates a fast computation on a vector processing computer.
Molecular dynamics of flow in micropores
Authors: Bitsanis I. , Magda J. J. , Tirrell M. , Davis H. T.
Published: July 2002

The method of nonequilibrium molecular dynamics is used to study the viscosity and flow properties of strongly inhomogeneous liquids, a particular case of which is a liquid confined in a micropore only a few molecular diameters wide. Fluid inhomogeneity is introduced by imposing an external potential that in one case simulates flat solid walls and in the other case causes density peaks in the middle of a thin liquid film. For comparison a homogeneous fluid is also simulated. In both types of inhomogeneous fluid, the shear stress and effective viscosity are smaller than in the homogeneous fluid. The density profiles and the diffusivities in the micropore were found to be independent of flow, even at the extremely high rates, 1010–1011 s−1 of the simulation. The Green–Kubo relation is found to be valid for the diffusivity under the flow studied. We propose a local average density model (LADM) of viscosity and diffusivity, in which the local transport coefficients are those of homogeneous fluid at a mean density obtained by averaging the local density over a molecular volume. LADM predicts qualitatively correct velocity profiles, effective viscosities, and shear stresses using only equilibrium density profiles and molecular diameters. An analogous local equilibrium version of Enskog’s theory of diffusivity agrees well with the simulated pore diffusivities. Recently Vanderlick and Davis generalized Enskog’s theory of diffusivity to strongly inhomogeneous fluids. Their theoretical pore diffusion coefficient is also in good agreement with simulation results.
A tractable molecular theory of flow in strongly inhomogeneous fluids
Authors: Bitsanis I. , Vanderlick T. K. , Tirrell M. , Davis H. T.
Published: July 2002

A recently introduced model is used to study several flows in fluids with large density variations over distances comparable to their molecular dimensions (strongly inhomogeneous fluids). According to our model, the local average density model (LADM), local viscosity coefficients can be assigned at each point in a strongly inhomogeneous fluid and the stress tensor retains its Newtonian form provided that the properly defined local viscosities are used. The model has been previously shown to agree with the results of molecular dynamics simulations on diffusion and flow properties in plane Couette flow. Application of this model requires determination of the molecular density profiles in the flow region. Using a successful closure for the pair distribution function, we solve the Yvon–Born–Green (YBG) equation of fluid structure in order to determine the density profiles of a fluid confined between planar micropore walls only a few molecular diameters apart. The fluid confinement produces a strongly inhomogeneous structure. Subsequently we apply LADM to set up the fluid mechanical equations for Couette flow, Poiseuille flow, and squeezing flow between parallel plates. With the use of the YBG theoretical density profiles we solve the flow equations and predict velocity profiles, stress distributions, and effective viscosities. The dependence of these quantities on the fluid inhomogeneity is described. The effective viscosity of strongly inhomogeneous fluids is found to be quite sensitive to the nature of the flow. Our squeezing flow analysis provides a first explanation of recent experimental findings on the effective viscosity of simple fluids confined in very narrow spaces.
The potential surface and stretching frequencies of X̃ 3B1 methylene (CH2) determined from experiment using the Morse oscillator-rigid bender internal dynamics Hamiltonian
Authors: Jensen Per , Bunker P. R.
Published: July 2002

The Morse oscillator-rigid bender internal dynamics (MORBID) Hamiltonian [P. Jensen, J. Mol. Spectrosc. 128, 478 (1988)] has been used in a fitting to all extant rotation–vibration data for X̃ 3B1 methylene CH2. This fitting leads to an improved determination of the potential energy surface, and in particular to reliable predictions for the stretching frequencies. We predict ν1=2992 cm−1 and ν3=3213 cm−1 for 12CH2, and we hope that the new predictions will encourage the experimental search for these weak fundamentals. In the MORBID approach the rotation–vibration energies are obtained from the potential energy surface in a purely variational calculation, and consequently the present work is an improvement over previous determinations of the CH2 potential energy surface from experiment that used the nonrigid bender formalism [see P. R. Bunker et al., J. Chem. Phys. 85, 3724 (1986), and references therein]; this latter approach treats the stretching vibrations by second order perturbation theory. A fitting to the J=0 vibrational energy data for ã 1A1 methylene has also been made here using the MORBID Hamiltonian. Combining the results of these MORBID fittings to experimental data for the (X̃) and (ã) states of CH2 we obtain the singlet–triplet splittings T0(ã 1A1)=3147 cm−1 (8.998 kcal/mol) and Te(ã 1A1)=3223 cm−1 (9.215 kcal/mol).
An efficient internally contracted multiconfiguration–reference configuration interaction method
Authors: Werner Hans-Joachim , Knowles Peter J.
Published: July 2002

A new internally contracted direct multiconfiguration–reference configuration interaction (MRCI) method is described which allows the use of much larger reference spaces than any previous MRCI method. The configurations with two electrons in the external orbital space are generated by applying pair excitation operators to the reference wave function as a whole, while the singly external and internal configurations are standard uncontracted spin eigenfunctions. A new efficient and simple method for the calculation of the coupling coefficients is used, which is well suited for vector machines, and allows the recalculation of all coupling coefficients each time they are needed. The vector H⋅c is computed partly in a nonorthogonal configuration basis. In order to test the accuracy of the internally contracted wave functions, benchmark calculations have been performed for F−, H2O, NH2, CH2, CH3, OH, NO, N2, and O2 at various geometries. The deviations of the energies obtained with internally contracted and uncontracted MRCI wave functions are mostly smaller than 1 mH and typically 3–5 times smaller than the deviations between the uncontracted MRCI and the full CI. Dipole moments, electric dipole polarizabilities, and electronic dipole transition moments calculated with uncontracted and contracted MRCI wave functions also are found to be in close agreement. The efficiency of the method is demonstrated in large scale calculations for the CN, NH3, CO2, and Cr2 molecules. In these calculations up to 3088 reference configurations and up to 154 orbitals were employed. The biggest calculation is equivalent to an uncontracted MRCI with more than 78 million configurations.
The Fourier grid Hamiltonian method for bound state eigenvalues and eigenfunctions
Authors: Marston C. Clay , Balint-Kurti Gabriel G.
Published: July 2002

A new method for the calculation of bound state eigenvalues and eigenfunctions of the Schrödinger equation is presented. The Fourier grid Hamiltonian method is derived from the discrete Fourier transform algorithm. Its implementation and use is extremely simple, requiring the evaluation of the potential only at certain grid points and yielding directly the amplitude of the eigenfunctions at the same grid points.
Structure of phosphorus clusters using simulated annealing—P2 to P8
Authors: Jones R. O. , Hohl D.
Published: July 2002

The geometries of low-lying isomers of phosphorus clusters P2 to P8 have been calculated using a density functional (DF) method, combined with molecular dynamics (MD) and simulated annealing techniques. The structures and vibration frequencies are in excellent agreement with experiment in those cases (P2, P4) where spectroscopic data are available. A roof-shaped tetramer is a prominent structural unit in low-lying states of P5, P6, P7, and P8. Contrary to widespread belief, the most stable isomer of P8 is not cubic, but the ‘‘wedge’’ or ‘‘cradle’’ structure found as a structural unit in violet (monoclinic, Hittorf) phosphorus. The energetic ordering and geometrical shapes of the P8 isomers show striking analogies to the corresponding valence-isoelectronic hydrocarbons (CH)8 cubane, cuneane, and 2,2′:4,4′-bis-(bicyclobutyl). The bonding and structural trends in phosphorus clusters are discussed in detail.
Photoelectron spectroscopy and electronic structure of clusters of the group V elements. I. Dimers
Authors: Wang Lai-Sheng , Lee Y. T. , Shirley D. A. , Balasubramanian K. , Feng P.
Published: July 2002

The HeI (584 Å) high resolution photoelectron spectra of As+2, Sb+2, and Bi+2 have been obtained with a high temperature molecular beam source. A pure As2 beam was produced by evaporating Cu3As. Sb2 was generated as a mixture with the atoms and tetramers by evaporating the pure element, while Bi2 was generated as a mixture with only the atoms from the pure element. Vibrational structure was well resolved for the As+2 spectrum. Spectroscopic constants were derived and reported for the related ionic states. In addition, we have carried out relativistic complete active space self-consistent field followed by multireference single + double configuration interaction calculations on these dimers both for the neutral ground states and the related ionic states. The agreements between the calculated and experimentally derived spectroscopic constants were fairly good, although the calculations tended to underestimate consistently the strength of the bonding in these heavy homonuclear diatomics.
Maximal and minimal characteristics of molecular electrostatic potentials
Authors: Pathak Rajeev K. , Gadre Shridhar R.
Published: July 2002

Existence of strict local maxima within the molecular electrostatic potential (MESP) maps has been rigorously ruled out. The proof to this effect is based solely on the classical electrostatic Poisson equation. It has been further shown that at least one-directional negative-valued minimum in MESP for a negative molecular ion must occur along any arbitrary direction. Under some special circumstances, an equipotential MESP surface could exist for such a species. These results properly reduce to their atomic counterparts proven by Politzer and co-workers [Weinstein et al., Theor. Chim. Acta (Berl.) 38, 59 (1975); Sen and Politzer, J. Chem. Phys. 90, 4370 (1989)].
Self-diffusion in the compressed fluid lower alkanes: Methane, ethane, and propane
Authors: Greiner-Schmid A. , Wappmann S. , Has M. , Lüdemann H.-D.
Published: July 2002

Self-diffusion coefficients D for CH4, C2H6, and C3H8 have been measured at pressures up to 200 MPa and 450 K by the spin echo technique with pulsed field gradients. The experimental results for propane agree with data obtained by recent M. D. simulations with a three-site Lennard-Jones-skeleton model. In the p,T range studied, the experimental self-diffusion coefficients can be described quantitatively by the interacting sphere model and the rough hard sphere model. This implies, that even a single Lennard-Jones potential and diameter can represent the dynamic data for propane quantitatively.
Second-order perturbation theory with a complete active space self-consistent field reference function
Authors: Andersson Kerstin , Malmqvist Per-Åke , Roos Björn O.
Published: July 2002

The recently implemented second-order perturbation theory based on a complete active space self-consistent field reference function has been extended by allowing the Fock-type one-electron operator, which defines the zeroth-order Hamiltonian to have nonzero elements also in nondiagonal matrix blocks. The computer implementation is now less straightforward and more computer time will be needed in obtaining the second-order energy. The method is illustrated in a series of calculations on N2, NO, O2, CH3, CH2, and F−.
Computed self-consistent field and singles and doubles configuration interaction spectroscopic data and dissociation energies for the diatomics B2, C2, N2, O2, F2, CN, CP, CS, PN, SiC, SiN, SiO, SiP, and their ions
Authors: McLean A. D. , Liu B. , Chandler G. S.
Published: July 2002

Single configuration self-consistent field (SCF) calculations near the Hartree–Fock limit, and singles and doubles configuration-interaction (CI)(SDCI) calculations from this single SCF configuration have been performed for the ground and selected excited states of the molecules B2+, B2, C2+, C2, N2+, N2, O2+, O2, F2+, F2, CN, CN−, CP, CS, PN, SiC, SiC−, SiN, SiN−, SiO, and SiP. Potential energy curves, with Davidson corrections, have been obtained around equilibrium separations. Equilibrium bond lengths, vibrational energies, ionization potentials, and dissociation energies are reported.
Infrared spectra of matrix isolated ClCO and a
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o calculation
Authors: Schnöckel Hansgeorg , Eberlein Robert A. , Plitt Harald S.
Published: July 2002

Cl atoms and CO molecules were trapped in a solid Ar matrix at 16 K. The formation of ClCO was followed via its IR spectrum. The vibrational frequencies of 35Cl12C16O were observed at 1876.7, 570.1, and 334.6 cm−1. Experiments with different CO isotopomers were performed in order to confirm the assignment of the absorptions and to characterize the force field. The results extend and correct earlier data [M. E. Jacox and D. E. Milligan, J. Chem. Phys. 43, 866 (1965)]. With the help of quantum chemical calculations (UHF, MP2), the optimized ClCO bond angle was obtained to be 129.2°. The computed bond lengths were determined to be 1.159 Å for C–O and 1.807 Å for C–Cl. Based on force constant calculations, the C–Cl bond in ClCO was found to be extremely weak compared to that in Cl2CO.
Nuclear dynamics of decaying states: A time-dependent formulation
Authors: Cederbaum L. S. , Tarantelli F.
Published: July 2002

The wave packet dynamics accompanying the excitation to a decaying electronic state and the subsequent decay to final electronic states are discussed. The cross sections for the excitation and for the production of final states are related to the corresponding wave packets. The time-dependent formulation adds insight into the process and is amenable to semiclassical approximations and interpretations. It can also be used to compute the gross features of the observed spectra via a spectral moment expansion. An illustrative application demonstrates the usefulness of the expansion.
Rotational spectrum and structure of Ne–C6H6–H2O, an aromatic sandwich
Authors: Arunan E. , Emilsson T. , Gutowsky H. S.
Published: July 2002

Low J(J=1→5) rotational spectra of seven isotopomers of Ne–C6H6–H2O trimer have been observed with a Balle/Flygare Fourier transform microwave spectrometer. The trimer is found to be a symmetric top with a B0, DJ, and DJK in the parent of 959.3504(1) MHz, 2.425(2) kHz, and 13.385(5) kHz. The benzene is sandwiched between Ne and H2O, both of which lie on the C6 axis of benzene. Substitution analysis gives the neon and oxygen distances from the trimer center of mass (c.m.) to be 3.324 and 3.454 Å, respectively. The Ne to c.m. (C6H6) and c.m. (C6H6) to c.m. (H2O) distances thereby determined are 3.391 and 3.334 Å, respectively. Those in the corresponding dimers are 3.458 and 3.329 Å, giving a decrease in the trimer of 0.067 Å in the Ne to c.m. (C6H6) distance and an increase of 0.005 Å in c.m. (C6H6) to c.m. (H2O). Otherwise the state of the water in the dimer does not appear to be materially affected by addition of the Ne.
Energy-adjusted pseudopotentials for the actinides. Parameter sets and test calculations for thorium and thorium monoxide
Authors: Küchle W. , Dolg M. , Stoll H. , Preuss H.
Published: July 2002

We present nonrelativistic and quasirelativistic energy-adjusted pseudopotentials, the latter augmented by spin–orbit operators, as well as optimized (12s11p10d8f)/ [8s7p6d4f]-Gaussian-type orbitals (GTO) valence basis sets for the actinide elements actinium through lawrencium. Atomic excitation and ionization energies obtained by the use of these pseudopotentials and basis sets in self-consistent field (SCF) calculations differ by less than 0.2 eV from corresponding finite-difference all-electron results. Large-scale multiconfiguration self-consistent field (MCSCF), multireference configuration interaction (MRCI), and multireference averaged coupled-pair functional (MRACPF) calculations for thorium and thorium monoxide yield results in satisfactory agreement with available experimental data. Preliminary results from spin–orbit configuration interaction calculations for the low-lying electronic states of thorium monoxide are also reported.
Benchmark calculations with correlated molecular wave functions. IV. The classical barrier height of the H+H2→H2+H reaction
Authors: Peterson Kirk A. , Woon David E. , Dunning Thom H.
Published: July 2002

Using systematic sequences of correlation consistent Gaussian basis sets from double to sextuple zeta quality, the classical barrier height of the H+H2 exchange reaction has been calculated by multireference configuration interaction (MRCI) methods. The MRCI calculations for collinear H3 have also been calibrated against large basis set full CI (FCI) results, which demonstrate that the MRCI treatment leads to energies less than 1 μhartree (≤0.001 kcal/mol) above the FCI energies. The dependence of both the H2 and H3 total energies on the basis set is found to be very regular, and this behavior has been used to extrapolate to the complete basis set (CBS) limits. The resulting estimate of the H–H–H CBS limit yields a classical barrier height, relative to exact H+H2, of 9.60±0.02 kcal/mol; the best directly calculated value for the barrier is equal to 9.62 kcal/mol. These results are in excellent agreement with recent quantum Monte Carlo calculations.
Effects of chain topology on polymer dynamics: Bulk melts
Authors: Shaffer J. Scott
Published: July 2002

We introduce a new lattice-based Monte Carlo model of polymer dynamics in which the polymer chain topology can be altered without perturbing any static properties or the local segment mobility. Chain entanglements can then simply be switched ‘‘on’’ and ‘‘off,’’ and their effects on global dynamics can be clearly isolated. Two sets of simulations have been conducted for bulk polymer melts. In the first set chain crossing is rigorously forbidden, but in the second set the polymer chains are allowed to cross through each other. When the chains are not allowed to cross, the self-diffusion coefficient exhibits the classic signature of the crossover from unentangled to entangled dynamics. For short chains, D∼N−1, while for long chains, D∼N−2, where D is the diffusion coefficient and N is the number of polymer segments. Furthermore, the longest noncrossing chains show a clear preference for anisotropic motion along their own contours—they appear to move by reptation. When the chains are allowed to cross, however, D∼N−1 at all chain lengths, characteristic of unentangled dynamics. No crossover is indicated in this case, and no signs of reptation are present. Since the structure and local mobility are nearly identical in the two cases, the dynamical differences are due only to the chain topology through the crossing condition. We discuss how the results illustrate the role of entanglements in bulk polymers and how the model may be used in the future as a tool to examine entanglement effects in adsorbed layers and confined polymer fluids.
Electrostatic decoupling of periodic images of plane-wave-expanded densities and derived atomic point charges
Authors: Blöchl P. E.
Published: July 2002

The density of a molecule expanded in plane waves is decoupled from its periodic images using a fit to atom-centered Gaussians, which reproduces the long-range electrostatic potential of the original density. The interaction energy between the cluster and its periodic images is calculated by an Ewald summation. The method has been applied to self-consistent ab initio molecular dynamics calculations of charged and polar molecules. An atomic point charge model of the charge density is obtained, which can be used for classical molecular dynamics models and to couple classical and quantum mechanical simulations.
Ab initio molecular orbital model of scanning tunneling microscopy
Authors: Fujita Taro , Nakai Hiromi , Nakatsuji Hiroshi
Published: July 2002

An ab initio model of scanning tunneling microscopy (STM) is presented in the framework of the perturbation theory of Bardeen. The tip and sample are represented by the cluster model, and the first-order wave functions are calculated by ab initio Hartree–Fock (HF), configuration interaction (CI), and symmetry adapted cluster (SAC)/SAC-CI methods. This model was applied to simple tip–sample systems such as Pd2–Ag2, Pd2–C6H6, Pd2–(C6H6)2, and Li2–Li2. The calculated STM images were related to the HOMO, LUMO, etc. orbital symmetries of the tip–sample systems. The contribution of the Rydberg orbital was examined at different tip–sample distances. Electron correlations were found to modify the behavior of the tunneling transition probability of the Li2–Li2 system vs that calculated by the HF method.
Computer simulation studies of anisotropic systems. XXVI. Monte Carlo investigations of a Gay–Berne discotic at constant pressure
Authors: Bates M. A. , Luckhurst G. R.
Published: July 2002

The majority of molecules which form liquid crystals are elongated in shape. However, disk shaped molecules have also been shown to exhibit liquid crystalline phases. In this paper we report a series of constant pressure Monte Carlo simulations of model discotic molecules. We have used the Gay–Berne potential, which is in essence an anisotropic version of a shifted Lennard-Jones potential, to model the interactions between the disks. Initially we studied a system of 512 molecules over a range of pressures to determine the mesophases formed and to construct the phase diagram. The system was found to exhibit isotropic, nematic, and columnar phases. We have also studied a larger system of 2000 molecules at a single pressure to calculate more accurately the distribution functions used to describe the translational and orientational order within the various phases.
Statistical associating fluid theory for chain molecules with attractive potentials of variable range
Authors: Gil-Villegas Alejandro , Galindo Amparo , Whitehead Paul J. , Mills Stuart J. , Jackson George , Burgess Andrew N.
Published: July 2002

A version of the statistical associating fluid theory (SAFT) is developed for chain molecules of hard-core segments with attractive potentials of variable range (SAFT-VR). The different contributions to the Helmholtz free energy are evaluated according to the Wertheim perturbation theory. The monomer properties are obtained from a high-temperature expansion up to second order, using a compact expression for the first-order perturbation term (mean-attractive energy) a1. Making use of the mean-value theorem, a1 is given as the van der Waals attractive constant and the Carnahan and Starling contact value for the hard-sphere radial distribution function in terms of an effective packing fraction. The second-order perturbation term a2 is evaluated with the local compressibility approximation. The monomer cavity function, required for the calculation of the free energy due to the formation of the chains and the contribution due to association, is given as a function of a1. We analyse the equation of state for chain molecules with three different types of monomer hard-core potentials with variable attractive range: square-well (SW), Yukawa (Y), and Sutherland (S). The theory for the hard-core potentials can easily be generalised to soft-core systems: we develop a simple equation of state for Mie m−n potentials, of which the Lennard-Jones (LJ) 6-12 potential is a particular case. The equations of state, expressed in terms of reduced variables, are explicit functions of the reduced temperature, the packing fraction, the number of monomers segments forming the chain, and the parameter λ which characterises the range of the the attractive potential. The relevance of the last parameter in the application of the theory to n-alkanes and n-perfluoroalkanes is explicitly shown with the SW expressions. An accurate description of the vapour pressure and the saturated liquid densities is obtained, with a simple dependence of the parameters of the monomer potential on the number of carbons. The extension of our SAFT-VR expressions to mixtures is also presented in terms of a simple expression for the mean-attractive energy for mixtures, based on a straightforward generalisation of the theory for pure components.
Liquid–liquid phase separation in supersaturated lysozyme solutions and associated precipitate formation/crystallization
Authors: Muschol Martin , Rosenberger Franz
Published: July 2002

Using cloud point determinations, the phase boundaries (binodals) for metastable liquid–liquid (L–L) separation in supersaturated hen egg white lysozyme solutions with 3%, 5%, and 7% (w/v) NaCl at pH=4.5 and protein concentrations c between 40 and 400 mg/ml were determined. The critical temperature for the binodal increased approximately linearly with salt concentration. The coexisting liquid phases both remained supersaturated but differed widely in protein concentration. No salt repartitioning was observed between the initial and the two separated liquid phases. After the L–L separation, due to the presence of the high protein concentration phase, crystallization occurred much more rapidly than in the initial solution. At high initial protein concentrations, a metastable gel phase formed at temperatures above the liquid binodal. Both crystal nucleation and gel formation were accelerated in samples that had been cycled through the binodal. Solutions in the gel and L–L regions yielded various types of precipitates. Based on theoretical considerations, previous observations with other proteins, and our experimental results with lysozyme, a generic phase diagram for globular proteins is put forth. A limited region in the (T,c) plane favorable for the growth of protein single crystals is delineated.
Molecular density functional calculations in the regular relativistic approximation: Method, application to coinage metal diatomics, hydrides, fluorides and chlorides, and comparison with first-order relativistic calculations
Authors: van Wüllen Christoph
Published: July 2002

The application of the zeroth-order regular relativistic approximation (ZORA) for molecular density functional calculations is investigated. By introducing a model potential to construct the kinetic energy operator, stationarity of the energy with respect to orbital variations is gained and most problems connected with gauge dependence of the regular approximation are eliminated. The formulation of a geometry gradient is greatly facilitated using this formalism. Calculations for the coinage metal hydrides (CuH, AgH, AuH) as well as for the homonuclear (Cu2, Ag2, Au2) and heteronuclear (CuAg, CuAu, AgAu) diatomics show that the results of ZORA calculations within the electrostatic shift approximation, as introduced by van Lenthe and co-workers, can be duplicated using the simpler scheme proposed in this work. Results for the coinage metal fluorides (CuF, AgF, AuF) and chlorides (CuCl, AgCl, AuCl) are presented as well. First-order relativistic calculations have been performed for all systems to assess the applicability of leading-order relativistic perturbation theory.
Influence of polydispersity on the phase behavior of colloidal liquid crystals: A Monte Carlo simulation study
Authors: Bates Martin A. , Frenkel Daan
Published: July 2002

Using isobaric semigrand Monte Carlo simulations, we have investigated the phase behavior of a model for polydisperse rodlike colloids. The system consists of hard spherocylinders in the limit of infinite aspect ratio, with polydispersity in the length of the particles. If the polydispersity is small (standard deviation s<0.08), the phase behavior is essentially unchanged from that observed in monodisperse systems; thus nematic, smectic, and crystal phases are exhibited. For an intermediate range of polydispersities (0.08<s<0.18), the smectic phase is found to become increasingly destabilized with respect to the nematic phase at low densities and a columnar phase at high densities. This eventually leads to a terminal polydispersity (s≈0.18) above which the smectic phase is no longer stable. Beyond this value, only nematic and columnar phases are observed.
Spin-free relativistic no-pair ab initio core model potentials and valence basis sets for the transition metal elements Sc to Hg. Part I
Authors: Rakowitz Frank , Marian Christel M. , Seijo Luis , Wahlgren Ulf
Published: July 2002

Relativistic one-component ab initio core model potentials are presented for first-, second-, and third-row transition elements; corresponding valence spaces comprise the ns, (n−1)d, and (n−1)p shells. Direct relativistic effects on the valence electrons are explicitly taken into account by using one-component relativistic kinetic energy and Douglas–Kroll transformed no-pair nuclear attraction interaction operators. The Coulombic part of the atomic core–valence interaction has been fitted to the corresponding all-electron mean-field operators whereas a matrix representation has been chosen for the exchange part. While not involved in the fitting process, all-electron orbital energies and radial expectation values of the valence orbitals are very well reproduced in atomic model potential calculations. Molecular test calculations have been performed on selected transition metal oxides. Employing a [4s,4p,4d] contraction of the valence basis, excellent agreement between core model potential and all-electron no-pair results is achieved for bond distances, harmonic frequencies, and dissociation energies.
Density functional study of carbon clusters C2n (2⩽n⩽16). I. Structure and bonding in the neutral clusters
Authors: Jones R. O.
Published: July 2002

Density functional calculations have been performed for many isomers of neutral carbon clusters Cn (4⩽n⩽32, n even) using both local spin density (LSD) and gradient-corrected (Becke–Perdew) approximations to the exchange-correlation energy. The stable isomers include chains, rings, cages, and graphitic (“plate ” and “bowl”) structures, and we observe a fourfold periodicity in several structural classes as n changes. Stable cages exist for all clusters with n⩾8, and double rings are less stable than the monocyclic rings in all cases. Most planar structures have low-frequency out-of-plane vibrations. Gradient corrections often change the ordering of the energies of the isomers, but the effects are remarkably regular within a given structural type.
Segment density profiles of polyelectrolyte brushes determined by Fourier transform ellipsometry
Authors: Biesalski Markus , Rühe Jürgen , Johannsmann Diethelm
Published: July 2002

We describe a method for the explicit determination of the segment density profile φ(z) of surface-attached polymer brushes with multiple angle of incidence null-ellipsometry. Because the refractive index contrast between the brush layer and the solvent is weak, multiple reflections are of minor influence and the ellipsometric spectrum is closely related to the Fourier transform of the refractive index profile, thereby allowing for explicit inversion of the ellipsometric data. We chose surface-attached monolayers of polymethacrylic acid (PMAA), a weak polyelectrolyte, as a model system and determined the segment density profile of this system as a function of the pH value of the surrounding medium by the Fourier method. Complementary to the Fourier analysis, fits with error functions are given as well. The brushes were prepared on the bases of high refractive index prisms with the “grafting-from” technique. In water, the brushes swell by more than a factor of 30. The swelling increases with increasing pH because of a growing fraction of dissociated acidic groups leading to a larger electrostatic repulsion.
Solvent effect on vertical electronic transitions by the polarizable continuum model
Authors: Cossi Maurizio , Barone Vincenzo
Published: July 2002

A recent extension of the polarizable continuum solvation model (PCM) to excited electronic states is applied to the study of solvent effects on electronic transitions, accounting for both electrostatic and nonelectrostatic solute–solvent interactions. A general formalism for nonequilibrium electrostatic solvation is developed, applicable to all PCM versions, and a recent procedure for the quantum-mechanical computation of dispersion and repulsion solute–solvent interactions is implemented and used for the first time in this context. The procedure is applied to the study of the n→π* transition of acetone in aqueous and nonaqueous solvents: nonequilibrium effects are very important in polar environments; also, the inclusion of dispersion and repulsion is mandatory to obtain the correct trend of the solvatochromic shifts. The effect of adding some explicit solvent molecules is also analyzed.
Assessment of Gaussian-3 and density functional theories for a larger experimental test set
Authors: Curtiss Larry A. , Raghavachari Krishnan , Redfern Paul C. , Pople John A.
Published: July 2002

The G2/97 test set [J. Chem. Phys. 106, 1063 (1997)] for assessing quantum chemical methods used to predict thermochemical data is expanded to include 75 additional enthalpies of formation of larger molecules. This new set, referred to as the G3/99 test set, includes enthalpies of formation, ionization potentials, electron affinities, and proton affinities in the G2/97 set and 75 new enthalpies of formation. The total number of energies in the G3/99 set is 376. Overall, G3 theory has a mean absolute deviation of 1.07 kcal/mol for the G3/99 test set and does about as well for the new hydrocarbons and substituted hydrocarbons as it does for those in the G2/97 test. However, G3 theory has large deviations for several of the new nonhydrogen systems in the G3/99 test set such as SF6 and PF5. Part of the source of error is traced to the inadequate geometries used in G3 theory for these molecules. Other variations of G3 theory are also assessed such as G3(MP2), G3(MP3), and the versions of G3 theory using scaled energy terms instead of the higher level correction. These variations also do well for the larger hydrocarbons and substituted hydrocarbons, but fail for the same nonhydrogen systems as G3 theory. The density functional methods assessed in this study, including the hybrid B3LYP method, all have much larger deviations from experiment for the new enthalpies of formation in the expanded test set; the mean absolute deviation more than doubles compared to that for the enthalpies in the G2/97 test set. This is due to a cumulative effect of the errors in the larger molecules in the density functional methods.
Isotropic and anisotropic charged spheres admitting a one-parameter group of conformal motions
Authors: Herrera L. , Ponce de León J.
Published: July 2002

Some exact analytical solutions of the static Einstein–Maxwell equations for perfect and anisotropic fluids were found under the assumption of spherical symmetry and the existence of a one-parameter group of conformal motions. All solutions are matched to the Reissner‘xnNordström metric and possess positive energy density larger than the stresses, everywhere within the sphere.
Multicomponent integrable reductions in the Kadomtsev–Petviashvilli hierarchy
Authors: Sidorenko Jurij , Strampp Walter
Published: July 2002

New types of reductions of the Kadomtsev–Petviashvili (KP) hierarchy are considered on the basis of Sato’s approach. Within this approach the KP hierarchy is represented by infinite sets of equations for potentials u2,u3,..., of pseudodifferential operators and their eigenfunctions Ψ and adjoint eigenfunctions Ψ*. The KP hierarchy was studied under constraints of the following type (∑ni=1 ΨiΨ*i)x = Sκ,x where Sκ,x are symmetries for the KP equation and Ψi(λi), Ψ*i(λi) are eigenfunctions with eigenvalue λi. It is shown that for the first three cases κ=2,3,4 these constraints give rise to hierarchies of 1+1-dimensional commuting flows for the variables u2, Ψ1,...,Ψn, Ψ*1,...,Ψ*n. Bi-Hamiltonian structures for the new hierarchies are presented.
Path integral approach to noncommutative space–times
Authors: Mangano Gianpiero
Published: July 2002

We propose a path integral formulation of noncommutative generalizations of space–time manifold in even dimensions, characterized by a length scale λP. The commutative case is obtaind in the limit λP=0.
Formal variable separation approach for nonintegrable models
Authors: Lou Sen-yue , Chen Li-Li
Published: July 2002

Using a formal variable separation approach, a nonlinear partial differential equation can be solved by solving ordinary different equations or even algebraic equations. Taking the KdV–Burgers and modified KdV–Burgers equations with background interaction as simple examples, some explicit solitary wave solutions which are induced by background source and nonlinearity or dispersion are obtained.
Nonequilibrium in statistical and fluid mechanics. Ensembles and their equivalence. Entropy driven intermittency
Authors: Gallavotti Giovanni
Published: July 2002

We present a review of the chaotic hypothesis and discuss its applications to intermittency in statistical mechanics and fluid mechanics proposing a quantitative definition. Entropy creation rate is interpreted in terms of certain intermittency phenomena. An attempt at a theory of the experiment of Ciliberto–Laroche on the fluctuation law is presented.
On mixing in an elliptic turbulent free jet
Authors: Quinn W. R.
Published: July 2002

This paper documents the results of an experimental study of the mean flow and turbulence characteristics of a turbulent free jet of air issuing, into still air surroundings, from a sharp-edged elliptical slot of aspect ratio 5. The measured quantities, which were obtained with hot-wire anemometry as a flow diagnostic tool, include the mean streamwise velocity, the turbulence intensities, the Reynolds shear stress, the transport of some of the Reynolds stresses, and the flatness and skewness of the distributions of the streamwise velocity fluctuations. Two switches of the major and minor axes were observed and it was found that the jet attains an axisymmetric shape at about 30 equivalent slot diameters downstream of the exit plane. Also, the jet, compared to a turbulent free jet from a sharp-edged round slot of the same exit area, was found to entrain ambient fluid faster both in the near and far flow fields.
Anomalous dispersion and finite-size effects in hydrodynamic dispersion
Authors: Bacri J.-C. , Rakotomalala N. , Salin D.
Published: July 2002

Anomalous dispersion refers to concentration profiles that exhibit long-time tails as opposed to normal or Gaussian dispersion, which does not exhibit such tails. An original acoustic technique has enabled experimentally the demonstration that, in an unsaturated porous medium, the observed non-Gaussian dispersion is due only to finite-size effects: the sample length is set too small to achieve a statistical Gaussian random walk. An accurate fit to the data with a semiphenomenological model is suitable for comparison with a nonlocal theory concerning this transient effect. Thus the mechanism involved in the dispersion process, and also, the characteristic length of this dispersion, can be determined.
Local energy transfer and nonlocal interactions in homogeneous, isotropic turbulence
Authors: Domaradzki J. Andrzej , Rogallo Robert S.
Published: July 2002

Detailed computations were made of energy transfer among the scales of motion in incompressible turbulent fields at low Reynolds numbers generated by direct numerical simulations. It was observed that although the transfer resulted from triad interactions that were nonlocal in k space, the energy always transferred locally. The energy transfer calculated from the eddy-damped quasinormal Markovian (EDQNM) theory of turbulence at low Reynolds numbers is in excellent agreement with the results of the numerical simulations. At high Reynolds numbers the EDQNM theory predicts the same transfer mechanism in the inertial range that is observed at low Reynolds numbers, i.e., predominantly local transfer caused by nonlocal triads. The weaker, nonlocal energy transfer is from large to small scales at high Reynolds numbers and from small to large scales at low Reynolds numbers.
Effect of static deformation and external forces on the oscillations of levitated droplets
Authors: Suryanarayana P. V. R. , Bayazitoglu Y.
Published: July 2002

The oscillations of an aspherical droplet subjected to different external forces are considered. For an arbitrary shape deformation, it is shown that the frequency spectrum splits into (2l−1) peaks for a mode l oscillation, and the splitting of the frequency spectrum is calculated for mode 2, 3, and 4 oscillations. The deformation is then treated as a consequence of a general external force, and the frequency split is obtained in terms of the external force parameters. Droplets levitated by acoustic, electromagnetic, and combined acoustic-electromagnetic forces are considered in particular, and it is shown that the effects of asphericity adequately explain the splitting of the frequency spectrum observed commonly in experiments. The interpretation of spectra with regard to accurate surface tension measurement using the oscillations of levitated droplets is discussed, and the results applied to some previous experimental results. It is shown that the accuracy of surface tension measurements can improve if the asphericity caused by the levitating force, and the resulting frequency split, are taken into account.
The stability of a sheared density interface
Authors: Lawrence G. A. , Browand F. K. , Redekopp L. G.
Published: July 2002

This study investigates the stability of stratified shear flows when the density interface is much thinner than, and displaced with respect to, the velocity interface. Theoretical results obtained from the Taylor–Goldstein equation are compared with experiments performed in mixing layer channels. In these experiments a row of spanwise vortex tubes forms at the level of maximum velocity gradient which, because of the profile asymmetry, is displaced from the mean interface level. As the bulk Richardson number is lowered from a high positive value the effects of these vortex tubes become more pronounced. Initially the interface cusps under their influence, then thin wisps of fluid are drawn from the cusps into asymmetric Kelvin–Helmholtz billows. At lower Richardson numbers increasingly more fluid is drawn into these billows. The inherent asymmetry of flows generated in mixing layer channels is shown to preclude an effective study of the Holmboe instability. Statically unstable flows (negative Richardson numbers) are subject to the Rayleigh–Taylor instability. However, if the absolute value of the Richardson number is sufficiently small the Kelvin–Helmholtz instability dominates initially.