Terms Of Interaction Energies Research Articles

Vortex pinning in a superconducting film due to in-plane magnetized ferromagnets of different shapes: The London approximation

The London approach is used to study the interaction between a superconducting vortex in a type-II superconducting film (SC) and a ferromagnet (FM) with in-plane magnetization. We calculated numerically the dependence of the pinning behavior on the FM-vortex distance, SC film thickness, and geometry of the magnetic structure and its magnetization. Dual behavior of the interaction energy in terms of the field-polarity-dependent pinning was found. For weak magnetization such that no vortex-antivortex pair is induced by the FM an external vortex will be pinned near the negative pole of the FM. In the presence of a vortex-antivortex pair the external vortex is pinned on the positive (negative) pole of the FM if the magnetization of the FM is below (above) some critical value. Further, we investigated the interaction of a vortex and an in-plane magnetic stripe (``wall''). Such SC-FM heterostructure is found to be useful in applications where vortex-free superconducting areas are needed. For a more complicated geometry of the FM, i.e., magnets with edge defects, we discuss the breaking of the vortex-FM interaction symmetry which results in different local minima for the energetically favorable vortex position.

Phase behaviors of symmetric polymer blend systems

AbstractThe modified double‐lattice model is extended to polymer blend systems. We redefine Cγ as a new universal function of interaction energy to reduce the mathematical defects that originate from the truncation of higher order interaction energy terms. We correlate Cγ with Ryu et al.'s numerical results for symmetric polymer blends with various chain lengths (r1 = r2 = 8, 20, 50, or 100). In addition, oriented interactions between polymer segments are considered with respect to the secondary lattice concept. The proposed model shows a good agreement with the experimental data. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1532–1538, 2004

Effect of pH on the Aggregation Stability of Microcrystalline Cellulose Dispersions in Aqueous 0.1 M NaCl Solutions

Effect of pH on the coagulation kinetics of microcrystalline cellulose dispersions in an aqueous 0.1 M NaCl solution is studied by the flow ultramicroscopy. The lowest coagulation rate is observed at pH 4.9. A decrease or an increase in pH gives rise to the coagulation rate approaching the rate of fast coagulation (according to Smoluchowski) at pH 1.0. Results of calculating the particle pair interaction energy in terms of the DLVO theory with allowance for only the molecular and ion electrostatic components suggest the dominance of attraction forces at any interparticle distances and cannot explain the data of experimental methods. The allowance for the structural component, which arises upon the overlap of water boundary layers surrounding hydrophilic particles of microcrystalline cellulose, makes it possible to treat the experimental results and estimate possible values of the K andl parameters of the equation for the structural component.

Estimation of Structural Characteristics during Drying of Molded Organic and Organomineral Biogenic Materials

Structuring processes during the drying of molded materials based on peat and sapropel are studied in terms of interparticle interaction energy. The structuring during drying occurs in two steps, which are governed by the ratio between the liquid and solid phases of the system. The change in structural characteristics is caused by a certain type of molecular interaction. The final state of the system is directly affected by the shrinkage rate and anisotropy emerging during molding and drying. It is shown that the fracture activation energy abruptly changes in the transition from one structuring step to the other. The mechanism of this process is considered at various ratios between the concentrations of the organic and mineral matters of disperse materials of biogenic origin.

Study on additive effective interaction between vertical Bloch lines

AbstractThe properties of hard magnetic domains in garnet bubble films were studied. The formula for the domain wall energy of circular hard magnetic domains was improved by adding an assumptive effective interaction energy term between vertical Bloch lines. This satisfactorily interpreted the behavior of hard domains subjected to a static bias magnetic field, which had remained unclear for many years, and also successfully interpreted the temperature character of the hard domains. Therefore, this assumptive effective interaction energy can act as a clue to derive exactly the interaction between vertical Bloch lines. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Excitonic level structures of LH1 and LH2 of purple photosynthetic bacteria using an analytical approach

The excitonic level structure of a ring-like chain of dimers is discussed analytically in order to aid the understanding of the possible spectral properties of LH1 and LH2 of purple photosynthetic bacteria. Under the approximation of dipole-dipole interaction between Bchls, the excitonic levels, bandwidths and energy gap between two Davydov subbands are expressed analytically in terms of interaction energies and configurational parameters of dipoles. Our model includes all the interactions between pigment molecules in the system. The oscillator strengths and circular dichroism (CD) for the excitonic states are also presented analytically. The simulated absorption and CD spectra of LH1 and LH2 complexes reproduce the main features of the measured results.

On the electron-pair nature of the hydrogen bond in the framework of the atoms in molecules theory

Delocalization indices, as defined in the atoms in molecules theory, have been calculated between hydrogen-bonded atoms in 20 molecular complexes that are formed between several H-donor and acceptor molecules. In general, the delocalization index associated to an intermolecular hydrogen bond depends on the interaction energy of the complex, but also on the nature of the H-donor and acceptor atoms. The intermolecular delocalization index appears to be strongly correlated to the orbital interaction energy term as obtained from an energy decomposition scheme based on conceptual Kohn–Sham theory. Both the atoms in molecules theory and the energy decomposition analysis allow for a characterization of the hydrogen bonds in these complexes. In general, both kinds of analysis reveal that hydrogen bonding in these systems is not an essentially electrostatic interaction.

Molecular Dynamics Study of Desulfovibrio africanus Cytochrome c3 in Oxidized and Reduced Forms

A 5-ns molecular dynamics study of a tetraheme cytochrome in fully oxidized and reduced forms was performed using the CHARMM molecular modeling program, with explicit water molecules, Langevin dynamics thermalization, Particle Mesh Ewald long-range electrostatics, and quantum mechanical determination of heme partial charges. The simulations used, as starting points, crystallographic structures of the oxidized and reduced forms of the acidic cytochrome c 3 from Desulfovibrio africanus obtained at pH 5.6. In this paper we also report structures for the two forms obtained at pH 8. In contrast to previous cytochrome c 3 dynamics simulations, our model is stable. The simulation structures agree reasonably well with the crystallographic ones, but our models show higher flexibility and the water molecules are more labile. We have compared in detail the differences between the simulated and experimental structures of the two redox states and observe that the hydration structure is highly dependent on the redox state. We have also analyzed the interaction energy terms between the hemes, the protein residues, and water. The direct electrostatic interaction between hemes is weak and nearly insensitive to the redox state, but the remaining terms are large and contribute in a complex way to the overall potential energy differences that we see between the redox states.

Optimal methods for calculation of the amount of intermolecular electron transfer

In order to determine the optimal methodology for evaluation of the magnitude of intermolecular charge transfer, several methods have been examined: Mulliken population, natural population analysis, atoms in molecules (AIM) as well as charges from electrostatic potentials using a grid-based method (Chelp and Chelpg) procedures using a series of correlation consistent cc-pVXZ (X=D, T, Q) basis sets within LCAO MO SCF, MP2, DFT, and coupled cluster theory levels. In contrast to previous nonconclusive comparative studies, the present calculations reveal close matching of the recently available experimental data for six Lewis acid-base adducts with theoretical values derived from the Chelpg approach, whereas for the remaining methods relative errors are almost doubled. On the other hand, AIM and Chelpg results display the best linear correlation coefficients with the experimental data. Since reasonably accurate Chelpg results could be already obtained with SCF or DFT B3LYP methods using cc-pVDZ, such an approach opens the way to study intermolecular charge transfer in larger molecular systems. Preliminary results obtained within cc-pVDZ basis set and B3LYP functional for pyridine-SO3 complex do not exceed relative error limits observed for other smaller complexes. Analysis of corresponding interaction energy components calculated consistently in the dimer basis set indicates significant role of electrostatic, exchange and delocalization contributions, with rather negligible correlation term. In contrast to previous findings, the experimentally observed amount of transferred charge seems not to correlate with any interaction energy term.

INS and IR study of intermolecular interactions at the fumed silica-polydimethylsiloxane interphase, Part 3. Sicica-siloxane adsorption complexes

A vibration spectra study of the interphase fumed silica andpolydimethylsiloxane (PDMS) particles highlights the microscopic interactionmechanisms in the system. This study involves an extended examination of bothfree silica and PDMS components as well of their adsorption complexes. Thepresent paper, deals with the vibrational analysis of adsorption complexes ofpolymethylsiloxanes and hydrophilic or trimethylsiloxy silylated fumed silica.Vibrations have been investigated involving both experimental andcomputational approaches. Experiments were performed in the framework ofinfrared (FTIR) and inelastic neutron scattering (INS and AWDS) techniques.Spectral interpretation was carried out on the basis of quantum chemical (QCh)semiempirical calculations using AM1 and PM3 parameterisation, and applicationof an original software program for spectra analysis, COSPECO, involvingdirect and inverse spectral problem solutions and spectrum assignments. Indescribing the silica-PDMS interphase, dodecamethylpentasiloxane (Si5) hasbeen used as a linear model of polydimethylsiloxane; its adsorption atdifferent surface coverages Θ on hydrophilic and trimethylsiloxy(TMS)-silylated fumed silicas has been studied. Both, the PDMS and silicacomponents in the adsorption complexes, have been examined using protonatedand deuterated methyl groups of substrate and adsorbate. Additionalinformation was evaluated from the adsorption of longer chain PDMS polymerson hydrophilic silica. The adxorption has a strong impact on the vibrationspectra of both the silica and siloxane. Additional impacts evolve from thedegree of silylation of the silica surface, and the siloxane coverage Θ. The changes in the spectra can be attributed to immobilisation of theadsorbed siloxane on the silica surface, as well as to a `pressure' effect ofthe TMS units of the silica caused by adsorbed PDMS. In terms of interactionenergies, classical H-bonding shows a minor contribution, while Van-der-Waalsforces mainly govern the system; for the latter Si-O dipole interactions alsopay a dominant role.

A continuous viscosity model for thin film lubrication

The thickness of adsorbed molecular layers is the most critical factor in studying thin film lubrication, and is a key feature that distinguishes thin from thick film lubrication analysis. A method is presented that enables the adsorbed layer thickness to be calculated. This is based on adsorption theory and expressed in terms of molecular interaction energies. A continuous cross-gap viscosity model incorporating the layer thickness is introduced and used to calculate the load capacity and frictional characteristics of a simple bearing operating in the thin film regime.

New evidence for through-space transmission of substituent effects in benzene derivativesElectronic supplementary information (ESI) available: Table S1 containing literature data for substituent constants and pKa values used in this work. See http://www.rsc.org/suppdata/p2/b1/b106418e/

Electrostatic interaction energies between dipolar substituents and dipolar or charged reaction sites are re-examined. At short interaction distances and given orientations, the point-dipole approximation is shown to introduce important errors. Exact expressions are derived for correcting current equations for both interaction types, including the Kirkwood–Westheimer equation. The parameter λ for describing para–meta ratios of substituent inductive or Electra effects in benzene derivatives is modelled in terms of electrostatic interaction energy. Using the new equations it is shown that parameter λ can take values smaller or greater than unity, approaching a value of 2 at very large distances. Experimental λ values are calculated using reliable literature data for the ionisation equilibria of substituted phenylethanoic and 3-phenylpropanoic acids in ethanol–water mixtures. Theoretical λ values for these reactions are obtained taking into account rotational and conformational changes in the corresponding carboxylate anions. From the good agreement between experimental and theoretical λ values, it is concluded that there is through-space transmission of substituent effects in benzene derivatives.

Towards rational design and synthesis of aluminophosphates with 2-D layer and 3-D open-framework structures

This work presents our current progress on the rational design and synthesis of aluminophosphates with 2-D layer and 3-D open-framework structures. For the design of theoretical structures, we take two ways, one is using building block construction strategy to construct new 2-D networks and 3-D open frameworks. The other is using computer modeling method to systematically enumerate the theoretical network structures. The templating abilities of various amines in the formation of 2-D network or 3-D open-framework aluminophosphates can be evaluated in terms of non-bonding interaction energies of the guest templates and the host inorganic networks or frameworks. This well assists in the rational synthesis of target materials, with the good examples as 2-D Al 3P 4O 16 3− anionic layers, and 3-D Al 4P 5O 19(OH) 2− open frameworks with structures analogous to AlPO–HDA (HDA: 1,6-hexanediamine). On the other hand, 3-D open framework can be rationally assembled by a lower-dimensional chain through incorporation of transition metal cations as illustrated by the successful synthesis of a 3-D open-framework nickel aluminophosphate [NiAlP 2O 8][C 2N 2H 9].

Solitons in a one-dimensional interacting Bose-Einstein system

A modified Gross-Pitaevskii approximation was introduced recently for bosons in dimension $d\le2$ by Kolomeisky {\it et al.} (Phys. Rev. Lett. {\bf 85} 1146 (2000)). We use the density functional approach with sixth-degree interaction energy term in the Bose field to reproduce the stationary-frame results of Kolomeisky {\it et al.} for a one-dimensional Bose-Einstein system with a repulsive interaction. We also find a soliton solution for an attractive interaction, which may be boosted to a finite velocity by a Galilean transformation. The stability of such a soliton is discussed analytically. We provide a general treatment of stationary solutions in one dimension which includes the above solutions as special cases. This treatment leads to a variety of stationary wave solutions for both attractive and repulsive interactions.

Effect of concentration of ion exchanger, plasticizer and molecular weight of cyanocopolymers on selectivity and sensitivity of Cu(II) ion selective electrodes

The potential response of cyanocopolymer based Cu 2+ ion selective electrodes has been studied as a function of concentration of ionophore (Schiff’s base complex), plasticizer (dioctylphthalate) and molecular weight of the cyanocopolymers. The concentration variation in electrode constituents has shown significant effect on the sensitivity, selectivity, detection limits, response time and extent of interference from foreign ions during potentiometric measurements of electroactive ions. Hydrophobic nature and high dipole moment of the employed cyanocopolymers have enhanced the average lifetime of the electrode and shown least interference from solution anions. Electrodes prepared with optimum amount of the ionophore (2.7×10 −2 mol kg −1), plasticizer (2.1×10 −3 mol kg −1) and cyanocopolymers (2.0 g) of molecular weight 59.565 kg mol −1 have shown a Nernstian slope of 27.59±0.053 mV per decade activity of the Cu 2+ ions with a response time of 13.00±0.002 s. These electrodes with optimized amount of constituents have shown working range of 2.5×10 −7 to 1.0×10 −2 mol dm −3 activities of the Cu 2+ ions. The electrodes response as a function of concentration variation of ionophore, plasticizer and molecular weights of cyanocopolymers have been explained in terms of ionophore interaction energy and plasticization of the polymer matrix.

Probing Host-Guest Interaction Energies in Solid Inclusion Compounds from Experimental Studies of Competitive Inclusion

An approach to assess host-guest interaction energies in solid inclusion compounds with tunnel host structures is described, based on experimental studies of competitive inclusion of two different types of potential guest molecules X(S) q X and X(S) r X (q ≠ r) within the host tunnel. The proportions (m and 1-m) of the two types of guest molecule included within the host tunnel depend on the proportions (γ and 1-γ) of the two types of guest in the external “pool” of potential guest molecules and the relative “affinities” (χ and 1/χ) of the host tunnel for including the two types of guest. Expressions linking χ, m and γ can be applied to determine χ directly from experimental measurements of m for inclusion compounds prepared with different values of γ. The value of χ depends on the intermolecular interaction energies per unit length of tunnel for the two types of guest molecule, and χ may be expressed in terms of the host-guest interaction energies for the spacer units S and the end-groups X, and the guest-guest (X…X) interaction energy. Preliminary experimental results for urea inclusion compounds containing binary mixtures of α,Ω-dibromoalkane guest molecules are presented.

Henry constants predicted using multipole expansion for the interaction energies

AbstractIn line with the former studies of our group concerning the ab initio (parameter‐free) calculation of adsorption‐related properties, a new simple and powerful method is presented and applied to the adsorption of N2, O2, CO, CO2, and C2H2 in zeolite Y. The calculation method is investigated and some refinements on the calculation strategy are introduced. The calculation method is based on the expansion of the interaction energy in terms of the multipole moments and polarizabilities. The molecular electrical properties were calculated at a high level on the B3LYP/cc‐aug‐pV(Q or 5)Z. A relationship between the van der Waals radius and the radius of an atom of the interacting molecule in a charge field is proposed. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 58–69, 2001

More efficient Brownian dynamics algorithms

We examine the relative efficiencies of three- algorithms for performing Brownian Dynamics simulations without many-body hydrodynamics. We compare the conventional Brownian Dynamics algorithm of Ermak (CBD), Smart Monte Carlo (SMC) which incorporates Boltzmann sampling into essentially a CBD procedure, and the Stochastic Runge Kutta (SRK) method. We show, using the repulsive potential φ(r) = ε(σ/r) n , where n = 36 and 72, that the SRK algorithm gives the most accurate short-time dynamics for the mean-square displacements. The SRK algorithm static and dynamical properties converge better with a reducing time step to the exact values, than those generated by the CBD algorithm; giving efficiency gains typically of a factor of 3–4. Both CBD and SMC have the incorrect sign for the first correction term to the mean square displacement in a time step, whereas the SRK algorithm gives essentially the exact solution to order Δt 2, where Δt is the simulation time step. In fact, these correction terms are almost equal and opposite in sign. Expressions for these terms were derived in terms of the average interaction energy per particle. The force, shear and bulk stress autocorrelation functions were calculated. The average energy per particle and time correlation functions at short time have values in excess of the exact values, while the corresponding quantities for SRK are below this. This difference in behaviour can be traced back to the extent of compliance of the particle trajectories with the exact expansion of the Smoluchowski equation. The accuracy, at a given value of the time step, of the stochastic algorithms can significantly depend on the form of the interaction potential between particles. It is also demonstrated that the long time limits of various correlation functions are fairly insensitive to a particular scheme (SRK or CBD) used in the simulations. All the correlation functions have a stretched exponential region at intermediate to long times, and the values of the exponents on density and force law steepness have been determined.

Rational Synthesis of Microporous Aluminophosphates with an Inorganic Open Framework Analogous to Al4P5O20H·C6H18N2

The suitable organic templates for the formation of 3-D interrupted open-framework aluminophosphate can be predicted in terms of nonbonding interaction energies of host−guest through molecular dynamics simulations by Cerius2. The prediction is well proven by the successful syntheses of Al4P5O19(OH)·C5N2H16 (1) and Al4P5O19(OH)·C4N3H15 (2) through rational selection of 1,5-pentanediamine and diethylenetriamine template molecules based on energy calculations. The structures of 1 and 2 are anionic Al4P5O19(OH)2- open-frameworks, which are analogous to Al4P5O20H·C6H18N2 (AlPO-HDA) with 12- and 8-membered ring intersecting channels. Single-crystal X-ray diffraction analysis shows that 1 crystallizes in the triclinic space group P1 with lattice parameters a = 9.2450(9) Å, b = 12.688(2) Å, c = 5.0657(5) Å, α = 96.02(1)°, β = 105.89(1)°, and γ = 102.88(1)°. The as-synthesized compound 2 is characterized by powder X-ray diffraction, ICP, MAS NMR, and TG analyses. It has an empirical formula of Al4P5O19(OH)·C4N3H15 and possesses the same open-framework structure as AlPO-HDA.

Comparative ab initio study of the structures, energetics and spectra of X−⋅(H2O)n=1–4 [X=F, Cl, Br, I] clusters

X − ⋅(H 2 O) n=1–4 [X=F, Cl, Br, I] have been studied using high level ab initio calculations. This extensive work compares the structures of the different halide water clusters and has found that the predicted minimum energy geometries for different cluster are accompanied by several other structures close to these global minima. Hence the most highly populated structures can change depending on temperature due to the entropy effect. As the potential surfaces are flat, the wide-ranging zero point vibrational effects are important at 0 K, and not only a number of low-lying energy conformers but also large amplitude motions can be important in determining structures, energies, and spectra at finite temperatures. The binding energies, ionization potentials, charge-transfer-to-solvent (CTTS) energies, and the O–H stretching frequencies are reported, and compared with the experimental data available. A distinctive difference between F−⋅(H2O)n and X−⋅(H2O)n (X=Cl, Br, I) is noted, as the former tends to favor internal structures with negligible hydrogen bonding between water molecules, while the latter favors surface structures with significant hydrogen bonding between water molecules. These characteristics are well featured in their O–H spectra of the clusters. However, the spectra are forced to be very sensitive to the temperature, which explains some differences between different spectra. In case of F−⋅(H2O)n, a significant charge transfer is noted in the S0 ground state, which results in much less significant charge transfer in the S1 excited state compared with other hydrated halide clusters which show near full charge transfers in the S1 excited states. Finally, the nature of the stabilization interactions operative in these clusters has been explained in terms of many-body interaction energies.