bluuebunny/crossref_metadata_2025 huggingface dataset:
The ultrafast structural response of solid parahydrogen: A complementary experimental/simulation investigation
Authors: Bonacina L. , Larrégaray P. , van Mourik F. , Chergui M.
Published: August 2006

We present a complete characterization, based on femtosecond pump-probe spectroscopy and molecular dynamics simulations, of the ultrafast dynamics of electronic bubble formation in solid parahydrogen upon impulsive excitation of impurity-doped sites, which correlate with the lowest Rydberg state of the NO impurity. The high temporal resolution of the experiment allows us to identify three time scales in the structural dynamics. A first ultrafast expansion (<150fs), associated with the release of ∼80% of the excess energy available to the system after excitation, is accompanied by a transient narrowing of the spatial distribution of the first shell of H2 molecules around the impurity. In a subsequent stage (up to ∼800fs), the cavity expansion slows down, and energy starts to flow irreversibly into the crystal. Finally, the lattice undergoes a slow structural reorganization at the impurity site (5–10ps). A weak low-frequency recurrence, probably associated with an elastic response of the crystal, is observed at ∼10ps. The absence of polarization dependence indicates that the dynamics is largely dominated by translational (radial) motions of the molecules surrounding NO and not by the rotational motion of the impurity. Molecular dynamics simulations with temperature corrections, to mimic zero-point fluctuations, fully support the experimental results and show that the bubble model is suited to describe the dynamics of the system. It appears that the response of the medium around the impurity at short times is typical of a liquid solvent rather than that of a solid.
Ion and polymer dynamics in polymer electrolytes PPO-LiClO4. I. Insights from NMR line-shape analysis
Authors: Vogel M. , Torbrügge T.
Published: August 2006

We investigate ion and polymer dynamics in polymer electrolytes PPO-LiClO4 performing H2 and Li7 NMR line-shape analysis. Comparison of temperature dependent Li7 and H2 NMR spectra gives evidence for a coupling of ion and polymer dynamics. H2 NMR spectra for various salt concentrations reveal a strong slowdown of the polymer segmental motion when the salt content is increased. The H2 NMR line shape further indicates that the segmental motion is governed by dynamical heterogeneities. While the width of the distribution of correlation times G(logτ) is moderate for low and high salt content, an extremely broad distribution exists for an intermediate salt concentration of 15:1 PPO-LiClO4. For the latter composition, a weighted superposition of two spectral components, reflecting the fast and the slow polymer segments of the distribution, describes the H2 NMR line shape over a broad temperature range. Analysis of the temperature dependent relative intensity of both spectral components indicates the existence of a continuous rather than a discontinuous distribution G(logτ). Such continuous distribution is consistent with gradual fluctuations of the local salt concentration and, hence, of the local environments of the polymer segments, whereas it is at variance with the existence of large salt-depleted and salt-rich domains featuring fast and slow polymer dynamics, respectively. Finally, for all studied PPO-LiClO4 mixtures, the H2 NMR line shape strongly depends on the echo delay in the applied echo-pulse sequence, indicating that the structural relaxation of the polymer segments involves successive rotational jumps about small angles γ<20°.
O 17 nuclear quadrupole coupling constants of water bound to a metal ion: A gadolinium(III) case study
Authors: Yazyev Oleg V. , Helm Lothar
Published: August 2006

Rotational correlation times of metal ion aqua complexes can be determined from O17 NMR relaxation rates if the quadrupole coupling constant of the bound water oxygen-17 nucleus is known. The rotational correlation time is an important parameter for the efficiency of Gd3+ complexes as magnetic resonance imaging contrast agents. Using a combination of density functional theory with classical and Car-Parrinello molecular dynamics simulations we performed a computational study of the O17 quadrupole coupling constants in model aqua ions and the [Gd(DOTA)(H2O)]− complex used in clinical diagnostics. For the inner sphere water molecule in the [Gd(DOTA)(H2O)]− complex the determined quadrupole coupling parameter χ1+η2∕3 of 8.7MHz is very similar to that of the liquid water (9.0MHz). Very close values were also predicted for the the homoleptic aqua ions of Gd3+ and Ca2+. We conclude that the O17 quadrupole coupling parameters of water molecules coordinated to closed shell and lanthanide metal ions are similar to water molecules in the liquid state.
Coordinate transformation methods to calculate state-to-state reaction probabilities with wave packet treatments
Authors: Gómez-Carrasco Susana , Roncero Octavio
Published: August 2006

A procedure for the transformation from reactant to product Jacobi coordinates is proposed, which is designed for the extraction of state-to-state reaction probabilities using a time-dependent method in a body-fixed frame. The method consists of several steps which involve a negligible extra computational time as compared with the propagation. Several intermediate coordinates are used, in which the efficiency depends on the masses of the atoms involved in the reaction. A detailed study of the relative efficiency of using reactant and product Jacobi coordinates is presented for several systems, and simple arguments are found depending on the masses of the atoms involved in the reaction. It is found that the proposed method is, in general, more efficient than the use of product Jacobi coordinates, specially for nonzero total angular momentum. State-to-state reaction probabilities are obtained for Li+FH→LiF+H and F+HO→FH+O collisions for several total angular momenta.
Density functional study of ion hydration for the alkali metal ions (Li+,Na+,K+) and the halide ions (F−,Br−,Cl−)
Authors: Krekeler Christian , Hess Berk , Delle Site Luigi
Published: August 2006

We performed first principles density functional calculations to study the effect of monovalent ions M+ (M=Li,Na,K) and A− (A=F,Cl,Br) in water with the aim of characterizing the local molecular properties of hydration. For this reason, several ion-water clusters, up to five or six water molecules were considered; such structures were optimized, and the Wannier analysis was then applied to determine the average molecular dipole moment of water. We found that with an increasing number of water molecules, the molecular polarization is determined by the water-water interaction rather than the water-ion interaction, as one would intuitively expect. These results are consistent with those obtained in previous density functional calculations and with other results obtained by employing classical polarizable water models. The main message of this work is that as one increases the number of molecules the average dipole moment of all water molecules and the ones in the first shell tends to the same value as the average of a similar sized cluster of pure water. This supports the use of nonpolarizable classical models of water in classical atomistic simulations.
Evaluation of intrinsic compressibility of proteins by molecular dynamics simulation
Authors: Mori Kazuki , Seki Yasutaka , Yamada Yutaka , Matsumoto Hiroki , Soda Kunitsugu
Published: August 2006

Molecular dynamics simulation has been performed on five native proteins in water to evaluate their intrinsic isothermal compressibilities βT,int. To identify physical factors contributing to protein compressibility, a general method is presented for analyzing the compressibility of mechanically inhomogeneous systems. The value of βT,int varies with protein species considerably: β-lactoglobulin (14.15×10−2GPa−1) is more than twice as compressible as ribonuclease A (6.77×10−2GPa−1). β-lactoglobulin and myoglobin (13.95×10−2GPa−1) have similar values of βT,int, but the mechanisms responsible for them are significantly different. The volume fluctuations of internal cavities and the magnitudes of the crosscorrelation between them are the key factors determining βT,int of proteins. Though the volume fractions of internal cavity for the five studied proteins are nearly equal to one another, the mean cavity compressibilities βT,cav vary considerably with protein species and range from 0.35to0.69GPa−1, which are much smaller than those of normal organic liquids such as methanol, ethanol, and benzene and close to that of glycerol (0.55GPa−1), a strongly associated liquid.
Free-energy landscape of alcohol driven coacervation transition in aqueous gelatin solutions
Authors: Gupta Amarnath , Reena  , Bohidar H. B.
Published: August 2006

Liquid-liquid phase separation of a homogeneous polyampholyte (gelatin) solution into a dense polymer-rich coacervate and the dilute supernatant phase is discussed through free-energy landscape formalism. We have evaluated the free energy and entropy of the system as it undergoes the phenomenon of simple coacervation, driven by the addition of a nonsolvent. Electrophoretic mobility (μ) and turbidity measurements were performed on 0.01% and 0.05%(w∕v) aqueous gelatin solutions that were driven towards coacervation by the addition of ethanol. The mobility of the polyampholyte molecules, which was typically μ≈0.38±0.02μm∕scm∕V in water, gradually reduced for the soluble intermolecular complexes to a plateau value of μ≈0.11±0.01μm∕scm∕V as the ethanol volume fraction equaled φns≈0.47±0.03, which coincided with the first appearance of coacervate droplets (coacervation transition) observed from turbidity measurements, a behavior found to be invariant of gelatin concentration. These results were used as input to the theoretical model to explicitly construct the free-energy landscape for a single gelatin chain and the global system comprising the polymer-rich coacervate and the dilute supernatant phase.
Free energy of the solid C60 fullerene orientational order-disorder transition
Authors: Chang Jaeeon , Sandler Stanley I.
Published: August 2006

The free energies of the orientationally ordered crystal phase of C60 at low temperatures and the disordered crystal phase at high temperatures are calculated to an accuracy of ±0.05kJ∕mol using the expanded ensemble Monte Carlo method with the potential model of Sprik et al. [J. Phys. Chem. 96, 2027 (1992)]. The order-disorder transition temperature at zero pressure is determined directly from these free energies, and is found to be consistent with the abrupt changes in configurational energy and unit cell size also found in simulation. A modification of the potential results in predictions of the transition temperature of 257K and the entropy change of 18.1J∕molK at this transition, which are in good agreement with the experimental values of 260K and 19J∕molK, respectively. The orientational distinguishability in the ordered phase and the indistinguishability in the disordered phase lead to a contribution to the entropy difference of kln60, with 60 being the symmetry number of C60. This quantum mechanical correction is important for the accurate prediction of the phase transition properties of the C60 crystals.
Rotational spectra of 1-chloro-2-fluoroethylene. II. Equilibrium structures of thecisandtransisomer
Authors: Puzzarini Cristina , Cazzoli Gabriele , Gambi Alberto , Gauss Jürgen
Published: August 2006

Equilibrium structures for the cis and trans isomer of 1-chloro-2-fluoroethylene are reported. The structures are obtained within a least-squares fit procedure using the available experimental ground-state rotational constants for various isotopic species of both forms. Vibrational effects were eliminated before the analysis using vibration-rotation interaction constants derived from computed quadratic and cubic force fields with the required quantum chemical calculations carried out using second-order Møller-Plesset perturbation as well as coupled-cluster (CC) theory. The semiexperimental or empirical equilibrium geometries obtained in this way agree well with the corresponding theoretical predictions obtained from CC calculations [at the CCSD(T) level] after extrapolation to the complete basis-set limit and inclusion of core-valence correlation corrections. The present results allow a detailed analysis of the geometrical differences between the two forms of 1-chloro-2-fluoroethylene. They are also compared to the structural data available for other halogenated ethylenes.
A femtosecond study of photoinduced electron transfer from dimethylaniline to coumarin dyes in a cetyltrimethylammonium bromide micelle
Authors: Ghosh Subhadip , Sahu Kalyanasis , Mondal Sudip Kumar , Sen Pratik , Bhattacharyya Kankan
Published: August 2006

Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline to coumarin dyes in cetyltrimethylammonium bromide (CTAB) micelle is studied using femtosecond upconversion spectroscopy. The rate of PET in a CTAB micelle is found to be highly nonexponential with components much faster (∼10ps) than the slow components of solvation dynamics. The ultrafast components of electron transfer exhibits a bell-shaped dependence on the free energy change which is similar to the Marcus inversion.
Chromophores in phenylenevinylene-based conjugated polymers: Role of conformational kinks and chemical defects
Authors: Hennebicq Emmanuelle , Deleener Caroline , Brédas Jean-Luc , Scholes Gregory D. , Beljonne David
Published: August 2006

The influence of chemical defects and conformational kinks on the nature of the lowest electronic excitations in phenylenevinylene-based polymers is assessed at the semiempirical quantum-chemical level. The amount of excited-state localization and the amplitude of through-space (Coulomb-like) versus through-bond (charge-transfer-like) interactions have been quantified by comparing the results provided by excitonic and supermolecular models. While excitation delocalization among conjugated segments delineated by the defects occurs in the acceptor configuration, self-confinement on individual chromophores follows from geometric relaxation in the excited-state donor configuration. The extent of excited-state localization is found to be sensitive to both the nature of the defect and the length of the conjugated chains. Implications for resonant energy transfer along conjugated polymer chains are discussed.
Nonlinear instabilities and pathways of rupture in thin liquid bilayers
Authors: Bandyopadhyay Dipankar , Sharma Ashutosh
Published: August 2006

A long-wave nonlinear analysis of dewetting of thin (<100nm) liquid bilayers on solid substrates is presented. The short and the long time dynamics, interfacial morphologies, and the pathways of rupture and dewetting are studied to assess the roles of interfacial energies, film thicknesses, and viscosities. The twin interfaces (liquid-liquid and liquid-air) of bilayers under the influence of attractive van der Waals forces show a variety of dewetting pathways which, depending on the interfacial energies and film thicknesses, initially start with one of the two basic modes of instability—in-phase bending and out-of-phase squeezing. These short time modes of evolution and the extent of relative deformations at the interfaces are predicted from the linear stability analysis and verified by the nonlinear simulations. Simulations also show that in the later nonlinear regime, the intermolecular and viscous forces can profoundly modify the initial mode of instability and its growth rate leading to different pathways of dewetting and late stage morphologies. The complex late time patterns such as embedded droplets, inversion of top and bottom phases, and encapsulation of one fluid into the other are also engendered by tuning the intermolecular forces.
Thermal conductivity of a polymerizing liquid
Authors: Venkateshan K. , Johari G. P.
Published: August 2006

Thermal conductivity κ of seven polymerizing liquids has been measured in real time at different temperatures, and calorimetry and dielectric spectroscopy of one liquid are performed to help interpret the results. As a covalently bonded linear chain or a network structure in the liquid grows, κ of the Debye equation initially increases with the polymerization time tpolym as the molecular weight, density, and sound velocity increase, as on cooling a liquid. The measured κ reaches a maximum and then decreases, thus showing a peak at a certain tpolym and finally becomes constant, which is not the true behavior of steady state κ. The dielectric relaxation time of the covalently bonded structure at the tpolym for the κ peak is less than 5s and the extent of polymerization is below the vitrification plateau value. The peak height increases when the pulse time for κ measurement is increased. An increase in the liquid’s temperature shifts the κ peak to a shorter tpolym. Liquid compositions polymerizing rapidly show a similar shift, and those polymerizing slowly or whose viscosity does not reach a high enough value show a small κ peak or none. The κ peak may be an artifact of the time dependence of heat capacity during the pulse time used for the κ measurement, as proposed for glasses and supercooled liquids, similar to the changes in other properties observed as an artifact of kinetic freezing/unfreezing. For a polymerizing liquid, the peak may additionally arise when the rate of increase in the elastic modulus becomes equal to the rate of decrease in equilibrium Cp. In either case, its appearance does not distinguish the Brownian motions’ slowing on polymerization from that on cooling or compressing a liquid.
Anomaly-free sets of fermions
Authors: Batra Puneet , Dobrescu Bogdan A. , Spivak David
Published: August 2006

We present new techniques for finding anomaly-free sets of fermions. Although the anomaly cancellation conditions typically include cubic equations with integer variables that cannot be solved in general, we prove by construction that any chiral set of fermions can be embedded in a larger set of fermions which is chiral and anomaly-free. Applying these techniques to extensions of the standard model, we find anomaly-free models that have arbitrary quark and lepton charges under an additional U(1) gauge group.
Slice imaging and velocity mapping using a single field
Authors: Papadakis Vassilios , Kitsopoulos Theofanis N.
Published: August 2006

In this study we demonstrate that it is possible to perform velocity mapping and slice imaging of charged particle products using a single field (two electrodes) improving on the multielectrode geometries of the past. The performance of this new geometry is competitive to the multielectrode ones, presently limited by detector “spot” resolution. For imaging both photoelectrons and photofragments a resolution of ∼1% in velocity is achieved without further software manipulation such as event counting. The advantages of this new design are its ability to focus large volumes, its achromaticity (very little sensitivity on photofragment velocities), independence of the laser beam position in the field perpendicular to the extraction field, and compactness. Using this new design we have studied the photodissociation dynamics of pyrrole at 243nm and show that internal conversion of electronically excited state molecules to the ground state is important even at such low excitation energies.
Enhanced ferroelectricity in Ti-doped multiferroic BiFeO3 thin films
Authors: Wang Yao , Nan Ce-Wen
Published: August 2006

Ti 4 + ion-doped BiFeO3 thin films were prepared by sol-gel spin-coating technique on (111)Pt∕Ti∕SiO2∕Si substrates. X-ray diffraction and scanning electron microscope revealed the single phase, and good surface and cross-section morphologies of the films, respectively. Leakage current density measurement indicated that the quality of the BiFeO3 films was improved by Ti4+ doping. By introducing a small amount of Ti ions into the sol-gel solution-processed BiFeO3 films, large enhancement in both remnant and saturation polarizations of the doped-BiFeO3 films in comparisons with the undoped BiFeO3 films was observed, due to the reduced leakage current, stabilization of the ferroelectric distortion by Ti4+, and more homogenous microstructure.
Observation of collapsing radiative shocks in laboratory experiments
Authors: Reighard A. B. , Drake R. P. , Dannenberg K. K. , Kremer D. J. , Grosskopf M. , Harding E. C. , Leibrandt D. R. , Glendinning S. G. , Perry T. S. , Remington B. A. , Greenough J. , Knauer J. , Boehly T. , Bouquet S. , Boireau L. , Koenig M. , Vinci T.
Published: August 2006

This article reports the observation of the dense, collapsed layer produced by a radiative shock in a laboratory experiment. The experiment uses laser irradiation to accelerate a thin layer of solid-density material to above 100km∕s, the first to probe such high velocities in a radiative shock. The layer in turn drives a shock wave through a cylindrical volume of Xe gas (at ∼6mg∕cm3). Radiation from the shocked Xe removes enough energy that the shocked layer increases in density and collapses spatially. This type of system is relevant to a number of astrophysical contexts, providing the potential to observe phenomena of interest to astrophysics and to test astrophysical computer codes.
Exciton structure in sodium doped zinc oxide quantum dots
Authors: Kshirsagar Sachin D. , Nikesh V. V. , Mahamuni Shailaja
Published: August 2006

Photoluminescence spectra of electrochemically grown ZnO quantum dots doped with Na were studied at low temperature. Incorporation of Na in ZnO quantum dot is confirmed by the appearance of yellow photoluminescence at about 572nm instead of commonly observable green luminescence at about 530nm. Chemical analysis also supported the inclusion of Na in ZnO quantum dots. Rich excitonic structure was observed in photoluminescence spectra of these ZnO quantum dots. The excitonic features are analyzed in view of the published work on bulk ZnO.
Nonlinear effects in the interaction of time-dependent fields and chiral systems: A computational investigation
Authors: Baranowska Angelika , Rizzo Antonio , Jansík Branislav , Coriani Sonia
Published: August 2006

The nonlinear changes induced in the refractive index and in the optical rotatory dispersion when radiation interacts with a chiral system are studied computationally. The molecular parameters describing these effects are determined for methyloxirane, employing Hartree-Fock and density functional frequency dependent analytical response theory, the latter with the use of Becke three-parameter Lee-Yang-Parr functional. Their contribution to several circular and axial birefringences, which could be observed in pump-and-probe experiments for various combinations of polarization status and propagation direction of the two beams, is ascertained.
Hybrid correlation models based on active-space partitioning: Seeking accurate O(N5) ab initio methods for bond breaking
Authors: Bochevarov Arteum D. , Temelso Berhane , Sherrill C. David
Published: August 2006

Møller-Plesset second-order (MP2) perturbation theory remains the least expensive standard ab initio method that includes electron correlation, scaling as O(N5) with the number of molecular orbitals N. Unfortunately, when restricted Hartree-Fock orbitals are employed, the potential energy curves calculated with this method are of little use at large interatomic separations because of the divergent behavior of MP2 in these regions. In our previous study [J. Chem. Phys. 122, 234110 (2005)] we combined the MP2 method with the singles and doubles coupled cluster (CCSD) method to produce a hybrid method that retains the computational scaling of MP2 and improves dramatically the shape of the MP2 curves. In this work we expand the hybrid methodology to several other schemes. We investigate a new, improved MP2-CCSD method as well as a few other O(N5) methods related to the Epstein-Nesbet pair correlation theory. Nonparallelity errors across the dissociation curve as well as several spectroscopic constants are computed for BH, HF, H2O, CH+, CH4, and Li2 molecules with the 6-31G* basis set and compared with the corresponding full configuration interaction results. We show that among the O(N5) methods considered, our new hybrid MP2-CCSD method is the most accurate and significantly outperforms MP2 not only at large interatomic separations, but also near equilibrium geometries.
Dissociation of the OCS+ ion in low-lying electronic states studied using multiconfiguration second-order perturbation theory
Authors: Chen Bo-Zhen , Chang Hai-Bo , Huang Ming-Bao
Published: August 2006

Complete active space self-consistent-field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) calculations with atomic natural orbital basis sets were performed to investigate the S-loss direct dissociation of the 1Π2(XΠ2), 2Π2(AΠ2), 1Σ+2(BΣ+2), 1Σ−4, 1Σ−2, and 1Δ2 states of the OCS+ ion and the predissociations of the 1Π2, 2Π2, and 1Σ+2 states. Our calculations indicate that the S-loss dissociation products of the OCS+ ion in the six states are the ground-state CO molecule plus the S+ ion in different electronic states. The CASPT2//CASSCF potential energy curves were calculated for the S-loss dissociation from the six states. The calculations indicate that the dissociation of the 1Σ−4 state leads to the CO+S+ (Su4) products representing the first dissociation limit; the dissociations of the 1Π2, 1Σ−2, and 1Δ2 states lead to the CO+S+(Du2) products representing the second dissociation limit; and the dissociations of the 2Π2 and 1Σ+2 states lead to the CO+S+(Pu2) products representing the third dissociation limit. Seams of the 1Π2−1Σ−4, 2Π2−1Σ−4, 2Π2−1Σ−2, 2Π2−1Δ2, and 1Σ+2−1Σ−4 potential energy surface intersections were calculated at the CASPT2 level, and the minima along the seams were located. The calculations indicate that within the experimental energy range (15.07–16.0eV) the 2Π2(AΠ2) state can be predissociated by 1Σ−4 forming the S+(Su4) ion and can undergo internal conversion to 1Π2 followed by the direct dissociation of 1Π2 forming S+(Du2) and that within the experimental energy range (16.04–16.54eV) the 1Σ+2(BΣ+2) state can be predissociated by 1Σ−4 forming the S+(Su4) ion and can undergo internal conversion to 2Π2 followed by the predissociation of 2Π2 by 1Σ−2 and 1Δ2 forming the S+(Du2) ion. These indications are in line with the experimental fact that both the Su4 and Du2 states of the S+ ion can be formed from the 2Π2 and 1Σ+2 states of the OCS+ ion.
Gaussian-type function set without prolapse for the Dirac-Fock-Roothaan equation (II): Hg80 through Lr103
Authors: Yamamoto Shigeyoshi , Tatewaki Hiroshi , Watanabe Yoshihiro
Published: August 2006

We present prolapse-free universal Gaussian-type basis sets for Hg80 through Lr103. The basis set is determined so that the Dirac-Fock-Roothaan total energy should decrease monotonically toward the numerical Dirac-Fock total energy. The difference between the Dirac-Fock-Roothaan total energy and the numerical Dirac-Fock total energy is less than 3×10−6hartree for H1 through No102, and less than 5×10−6hartree for Lr103. The exponents of the present sets are determined in an even-tempered manner, aiming to give total energy closer to the numerical Dirac-Fock value as the expansion term increases. The recommended set is expanded by (64, 64, 64, 46, 46, 46, 46) terms for (s+, p−, p+, d−, d+, f−, f+) symmetries, respectively. A practical set with (56, 48, 48, 36, 36, 36, 36) terms is also presented.
A state-specific polarizable continuum model time dependent density functional theory method for excited state calculations in solution
Authors: Improta Roberto , Barone Vincenzo , Scalmani Giovanni , Frisch Michael J.
Published: August 2006

An effective state specific (SS) model for the inclusion of solvent effects in time dependent density functional theory (TD-DFT) computations of excited electronic states has been developed and coded in the framework of the so-called polarizable continuum model (PCM). Different relaxation time regimes can be treated thus giving access to a number of different spectroscopic properties together with solvent relaxation energies of paramount relevance in electron transfer processes. SS and conventional linear response (LR) models have been compared for two benchmark systems (coumarin 153 and formaldehyde in different solvents) and in the limiting simple case of a dipolar solute embedded in a spherical cavity. The results point out the complementarity of LR and SS approaches and the advantages of the latter model especially for polar solvents. The favorable scaling properties of PCM-TD-DFT models in both SS and LR variants and their availability in effective quantum mechanical codes pave the route for the computation of reliable spectroscopic properties of large molecules of technological and/or biological interest in their natural environments.
Dynamics of lithium ions in bismuthate glasses: Influence of strontium ions
Authors: Dutta A. , Ghosh A.
Published: August 2006

The influence of strontium ions on the relaxation dynamics of lithium ions in bismuthate glasses has been investigated in the frequency range of 10Hzto2MHz. We have observed that the conductivity increases and the activation energy decreases with the increase of SrO content in the glass compositions with fixed Li2O content. We have also observed that the conductivity increases and the activation energy decreases when Sr2+ ions are replaced by Li+ ions, keeping the glass former content fixed. We have shown that the estimated mobile ion concentration is almost independent of temperature and SrO content in the compositions. We have further shown that a fraction of total lithium ions are mobile for all glass compositions. The results have been interpreted on the basis of the modification of the bismuthate network by the addition of SrO, which enhances the mobility of Li ions, without altering the mobile Li+ ion concentration. We have also shown that the conductivity relaxation in these glasses is independent of temperature and composition, and the nonexponential parameter is less than that for the lithium bismuthate glasses without SrO.
Smoluchowski equation and the colloidal charge reversal
Authors: Diehl Alexandre , Levin Yan
Published: August 2006

Smoluchowski equation and the Monte Carlo simulations are used to study the conditions leading to the reversal of the electrophoretic mobility. Zeta (ζ) potential is identified with the diffuse potential at the shear plane which, we argue, must be placed at least one ionic diameter away from the colloidal surface. For sufficiently strongly charged colloids, ζ potential changes sign as a function of the multivalent electrolyte concentration, resulting in a reversal of the electrophoretic mobility. This behavior occurs even for very small ions of 4Å diameter as long as the surface charge density of the colloidal particles is sufficiently large and the concentration of 1:1 electrolyte is sufficiently low.
Chemical oxygen-iodine laser with CO2 buffer gas
Authors: Antonov I. O. , Azyazov V. N. , Mezhenin A. V. , Popkov G. N. , Ufimtsev N. I.
Published: August 2006

The efficient power operation in a chemical oxygen-iodine laser for subsonic and supersonic modes has been demonstrated. It is shown that the substitution of the buffer gas N2 by CO2 does not cause any significant variation in the dependence of the output power on the degree of dilution of the active medium. The maximum power was 581W for the flow rate of molecular chlorine 22mMol∕s that corresponds to a chemical efficiency of ηchem=29%.
Propagation of arbitrarily shaped femtosecond laser pulses through a photonic crystal fiber
Authors: Talukder Aminul I. , Totsuka Kouki , Tomita Makoto
Published: August 2006

We produce femtosecond optical pulses of different shapes to investigate the linear pulse propagation through a photonic crystal fiber in a regime where the conventional group velocity has no meaning and show that the temporal positions of centroid of energy are the same for both arbitrary pulses and transform-limited coherent pulses. By the concept of net group delay we explain the propagation delay for both the cases despite the fact that transmitted pulses suffer a severe distortion in the fiber.
Light-harvesting function through one-by-one electron and hole transfer in a methane-lithium system
Authors: Kodama Yasunobu , Ohno Kaoru
Published: August 2006

Carrying out a semiclassical molecular dynamics simulation of a CH4–Li2 system by using the time-dependent local density approximation of the time-dependent density functional theory, we find that one-by-one electron and hole transfer takes place from CH4 to Li2 when an electron is excited in CH4. Probability of the transfer is low when the molecules are fixed, but it increases when the molecules are freely relaxed or Li2 has 1eV of initial velocity.
A proof of Jarzynski’s nonequilibrium work theorem for dynamical systems that conserve the canonical distribution
Authors: Schöll-Paschinger E. , Dellago C.
Published: August 2006

We present a derivation of the Jarzynski [Phys. Rev. Lett. 78, 2690 (1997)] identity and the Crooks [J. Stat. Phys. 90, 1481 (1998)] fluctuation theorem for systems governed by deterministic dynamics that conserves the canonical distribution such as Hamiltonian dynamics, Nosé-Hoover dynamics, Nosé-Hoover chains, and Gaussian isokinetic dynamics. The proof is based on a relation between the heat absorbed by the system during the nonequilibrium process and the Jacobian of the phase flow generated by the dynamics.
Solvent effects on resonant first hyperpolarizabilities and Raman and hyper-Raman spectra of DANS and a water-soluble analog
Authors: Shoute Lian C. T. , Woo Han Young , Vak Doojin , Bazan Guillermo C. , Myers Kelley Anne
Published: August 2006

The two-photon-resonant first hyperpolarizabilities associated with hyper-Rayleigh and hyper-Raman scattering are reported for 4-dimethylamino-4′-nitrostilbene in 1,4-dioxane, dichloromethane, acetonitrile, and methanol, and for an ionic analog, 4-N,N-bis(6″-(N,N,N-trimethylammonium)-hexyl)amino-4′-nitrostilbene dibromide in methanol and water. Resonance Raman and hyper-Raman excitation profiles are also measured and modeled. The resonance Raman and hyper-Raman spectra show very similar relative intensities which do not vary much as the excitation frequency is tuned across the lowest-energy strong linear absorption band, suggesting that a single resonant electronic state dominates the one- and two-photon absorptions in this region. The absorption, resonance Raman, and hyper-Raman profiles can be simulated reasonably well with a common set of parameters. The peak resonant ∣β∣2, measured by hyper-Rayleigh scattering, varies by about 50% over the range of solvents examined and shows a weak correlation with the linear absorption maximum, with the redder-absorbing systems exhibiting larger peak hyperpolarizabilities. The experimental hyper-Rayleigh intensities are higher than those calculated, possibly reflecting contributions from nonresonant electronic states.
Exact analytical solution to the relativistic Klein-Gordon equation with noncentral equal scalar and vector potentials
Authors: Yasuk F. , Durmus A. , Boztosun I.
Published: August 2006

We present an alternative and simple method for the exact solution of the Klein-Gordon equation in the presence of the noncentral equal scalar and vector potentials by using Nikiforov-Uvarov method. The exact bound state energy eigenvalues and corresponding eigenfunctions are obtained for a particle bound in a potential of V(r,θ)=α∕r+β∕(r2sin2θ)+γcosθ∕(r2sin2θ) type.
Coherent states expectation values as semiclassical trajectories
Authors: Dias N. C. , Miković A. , Prata J. N.
Published: August 2006

We study the time evolution of the expectation value of the anharmonic oscillator coordinate in a coherent state as a toy model for understanding the semiclassical solutions in quantum field theory. By using the deformation quantization techniques, we show that the coherent state expectation value can be expanded in powers of ℏ such that the zeroth-order term is a classical solution while the first-order correction is given as a phase-space Laplacian acting on the classical solution. This is then compared to the effective action solution for the one-dimensional ϕ4 perturbative quantum field theory. We find an agreement up to the order λℏ, where λ is the coupling constant, while at the order λ2ℏ there is a disagreement. Hence the coherent state expectation values define an alternative semiclassical dynamics to that of the effective action. The coherent state semiclassical trajectories are exactly computable and they can coincide with the effective action trajectories in the case of two-dimensional integrable field theories.
Minimum magnetizability principle
Authors: Tanwar Akhilesh , Pal Sourav , Ranjan Roy Debesh , Kumar Chattaraj Pratim
Published: August 2006

A new electronic structure principle, viz., the minimum magnetizability principle, has been proposed and also has been verified through ab initio calculations, to extend the domain of applicability of the conceptual density functional theory in explaining the magnetic interactions and magnetochemistry. This principle may be stated as “a stable configuration/conformation of a molecule or a favorable chemical process is associated with a minimum value of the magnetizability.” The behavior of paramagnetic and diamagnetic components has been separately studied.
Vibrational lifetimes of molecular adsorbates on metal surfaces
Authors: Krishna Vinod , Tully John C.
Published: August 2006

We report density functional theory calculations of electron-hole pair induced vibrational lifetimes of diatomic molecules adsorbed on metal surfaces. For CO on Cu(100), Ni(100), Ni(111), Pt(100), and Pt(111), we find that the C–O internal stretch and the bending modes have lifetimes in the 1–6ps range, and that the CO-surface stretch and the frustrated translational modes relax more slowly, with lifetimes >10ps for all cases except CO on Ni(111). This strong mode selectivity confirms earlier calculations for CO on Cu(100) and demonstrates that the trends carry over to other metal substrates. In contrast, for NO adsorbed on Pt(111), whereas we still find that the bending mode has the shortest lifetime, about 1.3ps, we predict the other three modes to have almost equal lifetimes of 8–10ps. Similarly, for CN adsorbed on Pt(111), we calculate that the internal stretching and molecule-surface stretching modes have approximately equal lifetimes of about 15ps. Our results are in reasonable agreement with experiment, where available. We discuss some of the underlying factors that may contribute to the observed mode selectivity with adsorbed CO and the altered selectivity with NO and CN.
Resonant electron transfer and luminescent enhancement in a toluene suspension of Si nanocrystals
Authors: Wu X. L. , Qiu T. , Hu D. S. , Huang G. S. , Yuan R. K. , Siu G. G. , Chu Paul K.
Published: August 2006

Efficient resonant electron transfer from the surface bonding structure to the conduction band of quantum confined Si nanocrystals is observed by Si nanocrystals in a toluene suspension. Based on the electron transfer mechanism, the enhancement of photoluminescence originates from the band-to-band recombination in the p-type Si nanocrystals suspended in a toluene solution. The energy levels of the electrons in the Si nanocrystals chemisorbed with toluene molecules are calculated using the method of linear combination of atomic orbitals, and the characteristics of the obtained density of states is in good agreement with the observed photoluminescence properties.
Self-consistent quantum mechanical model for the description of excitation energy transfers in molecules at interfaces
Authors: Curutchet Carles , Cammi Roberto , Mennucci Benedetta , Corni Stefano
Published: August 2006

In this paper we present a quantum mechanical model to study excitation energy transfers in molecular systems located in the vicinity of an interface. The model is based on an approximate solution of the time-dependent density functional theory equations and solvent effects are introduced in terms of the integral equation formalism version of the polarizable continuum model. A unique characteristic of this model is that environment induced polarizing effects on the interacting molecules and screening effects on their interaction are included in a coherent and self-consistent way. The model is applied to different situations of the ethylene dimer in the vicinity of an air/water interface and compared with an alternative quantum electrodynamics approach.
Coverage dependence and hydroperoxyl-mediated pathway of catalytic water formation on Pt (111) surface
Authors: Qi Liang , Yu Jianguo , Li Ju
Published: August 2006

Hydrogen oxidation on Pt (111) surface is modeled by density functional theory (DFT). Previous DFT calculations showed too large O2 dissociation barriers, but we find them highly coverage dependent: when the coverage is low, dissociation barriers close to experimental values (∼0.3eV) are obtained. For the whole reaction, a new pathway involving hydroperoxyl (OOH) intermediate is found, with the highest reaction barrier of only ∼0.4eV. This may explain the experimental observation of catalytic water formation on Pt (111) surface above the H2O desorption temperature of 170K, despite that the direct reaction between chemisorbed O and H atoms is a highly activated process with barrier ∼1eV as previous calculations showed.
Low temperature EPR spectra of the mesoscopic cluster V15: The role of antisymmetric exchange
Authors: Tsukerblat Boris , Tarantul Alex , Müller Achim
Published: August 2006

The low temperature EPR spectra of the unique nanometer-scale molecular magnet V15 are analyzed within the three-spin model preserving trigonal symmetry. The Hamiltonian includes isotropic and antisymmetric (AS) exchange interactions introduced by Dzyaloshinsky (Zh. Eksp. Teor. Fiz. 32, 1547 (1957) [Sov. Phys. JETP 5, 1259 (1957)]) and [Moria Phys. Rev. 120, 91 (1960)]. With the aid of pseudoangular momentum representation the exact selection rules for the EPR transitions are deduced. AS exchange in the frustrated triangular system gives rise to a first order zero-field splitting of two low lying spin doublets and to a second order splitting of the excited quadruplet. This leads to a peculiar series of strong intramultiplet transitions and weak intermultiplet transitions. We show that the intramultiplet transitions are allowed only when the vector of the AS exchange is normal to the plane of vanadium triangle, but the series of weak intermultiplet transitions are a consequence of the in-plane part of the AS exchange. We have revealed a special temperature dependence of the EPR pattern with a peculiar shape of the full spectrum. Experimental data on high-frequency EPR of V15 at ultralow temperature are discussed.
Photoinduced electron transfer and geminate recombination in the group head region of micelles
Authors: Glusac Ksenija , Goun Alexei , Fayer M. D.
Published: August 2006

A pump-probe spectroscopic study of photoinduced forward electron transfer and geminate recombination between donors and acceptors located in the head group regions of micelles is presented. The hole donor is octadecyl-rhodamine B (ODRB) and the hole acceptor is N,N-dimethyl-aniline (DMA). The experiments are conducted as a function of the DMA concentration in the dodecyltrimethylammonium bromide and tetradecyltrimethylammonium bromide micelles. In spite of the fact that the absorptions of both the ODRB radical and ground state bleach spectrally overlap with the ODRB excited state absorption, a procedure that makes it possible to determine the geminate recombination dynamics is presented. These experiments are the first to measure the dynamics of geminate recombination in micelles, and the experiments have two orders of magnitude better time resolution than previous studies of forward transfer. The experimental data are compared to statistical mechanics theoretical calculations of both the forward transfer and the geminate recombination. The theory includes important aspects of the topology of the micelle and the diffusion of the donor-acceptors in the micelle head group region. A semiquantitative but nonquantitative agreement between theory and experiments is achieved.
What can be learned about molecular reorientation from single molecule polarization microscopy?
Authors: Gelin M. F. , Kosov D. S.
Published: August 2006

We have developed a general approach for the calculation of the single molecule polarization correlation function C(t), which delivers a correlation of the emission dichroisms at time 0 and t. The approach is model independent and valid for general asymmetric top molecules. The key dynamic quantities of our analysis are the even-rank orientational correlation functions, the weighted sum of which yields C(t). We have demonstrated that the use of nonorthogonal schemes for the detection of the single molecule polarization responses makes it possible to manipulate the weighting coefficients in the expansion of C(t). Thus valuable information about the orientational correlation functions of the rank higher than the second can be extracted from C(t).
Oxygen adsorption on gold nanofacets and model clusters
Authors: Visart de Bocarmé T. , Chau T.-D. , Tielens F. , Andrés J. , Gaspard P. , Wang R. L. C. , Kreuzer H. J. , Kruse N.
Published: August 2006

We have studied oxygen interaction with Au crystals (field emitter tips) using time-resolved (atom-probe) field desorption mass spectrometry. The results demonstrate no adsorption to take place on clean Au facets under chosen conditions of pressures (p<10−4mbar) and temperatures (T=300–350K). Steady electric fields of 6V∕nm do not allow dissociating the oxygen molecule. The measured O2+ intensities rather reflect ionization of O2 molecules at critical distances above the Au tip surface. Certain amounts of Au–O2 complex ions can be found at the onset of Au field evaporation. Calculations by density functional theory (DFT) show weak oxygen end-on interaction with Au10 clusters (ΔE=0.023eV) and comparatively stronger interaction with Au1∕Au(100) model surfaces (ΔE=0.25eV). No binding is found on {210} facets. Including (positive) electric fields in the DFT calculations leads to an increase of the activation energy for oxygen dissociation thus providing an explanation for the absence of atomic oxygen ions from the field desorption mass spectra.
Field-induced CO adsorption and formation of carbonyl waves on gold nanotips
Authors: Visart de Bocarmé T. , Kruse N. , Gaspard P. , Kreuzer H. J.
Published: August 2006

We report a study of the adsorption and reaction of CO on a gold nanotip in high electrostatic fields. Field ion microscopy is used to investigate the emergence of a Au-carbonyl wave that is made visible with oxygen as the imaging gas. We set up a simple kinetic model that reproduces the adsorption wave and confirms that the presence of oxygen merely serves as an imaging gas and does not lead to field-induced oxidation of CO.
Cartan calculi on the quantum superplane
Authors: Çelik Salih
Published: August 2006

Cartan calculi on the extended quantum superplane are given. To this end, the noncommutative differential calculus on the extended quantum superplane is extended by introducing inner derivations and Lie derivatives.
Yang-Baxter maps and symmetries of integrable equations on quad-graphs
Authors: Papageorgiou Vassilios G. , Tongas Anastasios G. , Veselov Alexander P.
Published: August 2006

A connection between the Yang-Baxter relation for maps and the multidimensional consistency property of integrable equations on quad-graphs is investigated. The approach is based on the symmetry analysis of the corresponding equations. It is shown that the Yang-Baxter variables can be chosen as invariants of the multiparameter symmetry groups of the equations. We use the classification results by Adler, Bobenko, and Suris to demonstrate this method. Some new examples of Yang-Baxter maps are derived in this way from multifield integrable equations.