bluuebunny/crossref_metadata_2025 huggingface dataset:
The exchange-correlation potential in ab initio density functional theory
Authors: Bartlett Rodney J. , Grabowski Ireneusz , Hirata So , Ivanov Stanislav
Published: May 2005

From coupled-cluster theory and many-body perturbation theory we derive the local exchange-correlation potential of density functional theory in an orbital dependent form. We show the relationship between the coupled-cluster approach and density functional theory, and connections and comparisons with our previous second-order correlation potential [OEP-MBPT(2) (OEP—optimized effective potential)] [I. Grabowski, S. Hirata, S. Ivanov, and R. J. Bartlett, J. Chem. Phys. 116, 4415 (2002)]. Starting from a general theoretical framework based on the density condition in Kohn–Sham theory, we define a rigorous exchange-correlation functional, potential and orbitals. Specifying initially to second-order terms, we show that our ab initio correlation potential provides the correct shape compared to those from reference quantum Monte Carlo calculations, and we demonstrate the superiority of using Fock matrix elements or more general infinite-order semicanonical transformations. This enables us to introduce a method that is guaranteed to converge to the right answer in the correlation and basis set limit, just as does ab initio wave function theory. We also demonstrate that the energies obtained from this generalized second-order method [OEP-MBPT(2)-f] and [OEP-MBPT(2)-sc] are often of coupled-cluster accuracy and substantially better than ordinary Hartree–Fock based second-order MBPT=MP2.
Heterodyned fifth-order 2D-IR spectroscopy of the azide ion in an ionic glass
Authors: Fulmer Eric C. , Ding Feng , Zanni Martin T.
Published: May 2005

A heterodyned fifth-order infrared pulse sequence has been used to measure a two-dimensional infrared (2D-IR) spectrum of azide in the ionic glass 3KNO3:2Ca(NO3)2. By rephasing a two-quantum coherence, a process not possible with third-order spectroscopy, the 2D-IR spectra are line narrowed, allowing the frequencies, anharmonicities, and their correlations to be measured for the first four (ν=0-3) antisymmetric stretch vibrational levels. In this glass, the vibrational levels are extremely inhomogeneously broadened. Furthermore, the glass shifts the energy of the ν=3 state more than the others, causing an inhomogeneous distribution in the anharmonic constants that are partially correlated to the inhomogeneous distribution of the fundamental frequency. These effects are discussed in light of the strong interactions that exist between the charged solute and solvent. Since this is the first example of a heterodyned fifth-order infrared pulse sequence, possible cascaded contributions to the signal are investigated. No evidence of cascaded signals is found. Compared to third-order spectroscopies, fifth-order pulse sequences provide advanced control over vibrational coherence and population times that promise to extend the capabilities of ultrafast infrared spectroscopy.
Ground- and excited-state diatomic bond lengths, vibrational levels, and potential-energy curves from conventional and localized Hartree–Fock-based density-functional theory
Authors: Teale Andrew M. , Tozer David J.
Published: May 2005

Ground- and excited-state diatomic bond lengths, vibrational levels, and potential-energy curves are determined using conventional and localized Hartree–Fock (LHF)-based density-functional theory. Exchange only and hybrid functionals (with various fractions of exchange) are considered, together with a standard generalized gradient approximation (GGA). Ground-state bond lengths and vibrational wave numbers are relatively insensitive to whether orbital exchange is treated using the conventional or LHF approach. Excited-state calculations are much more sensitive. For a standard fraction of orbital exchange, N2 and CO vertical excitation energies at experimental bond lengths are accurately described by both conventional and LHF-based approaches, providing an asymptotic correction is present. Excited-state bond lengths and vibrational levels are more accurate with the conventional approach. The best quality, however, is obtained with an asymptotically corrected GGA functional. For the ground and lowest four singlet excited states, the GGA mean absolute errors in bond lengths are 0.006 Å (0.5%) and 0.011 Å (0.8%) for N2 and CO, respectively. Mean absolute errors in fundamental vibrational wavenumbers are 49 cm−1 (2.7%) and 68 cm−1 (5.0%), respectively. The GGA potential-energy curves are compared with near-exact Rydberg–Klein–Rees curves. Agreement is very good for the ground and first excited state, but deteriorates for the higher states.
Diffusion, relaxation, and chemical exchange in casein gels: A nuclear magnetic resonance study
Authors: Gottwald Antje , Creamer Lawrence K. , Hubbard Penny L. , Callaghan Paul T.
Published: May 2005

Water in protein/water mixtures can be described in terms of bound water and free water, by exchange between these two states, and by its exchange with appropriate sites on the protein. H1-NMR diffusion and relaxation measurements provide insights into the mobility of these states. T2 relaxation-time dispersions (i.e., T2 relaxation times at different echo pulse spacings) reveal additional information about exchange. We present a comprehensive set of diffusion and T2 dispersion measurements on casein gels for which the protein/water ratio ranges from 0.25 to 0.5. The combination of these methods, taken in conjunction with concentration dependence, allows a good estimate of the parameters required to fit the data with Luz/Meiboom and Carver/Richards models for relaxation and chemical exchange. We compare the exchange (a) between water and protein and (b) between free water and bound water. Further, we attempt to distinguish chemical site exchange and diffusion/susceptibility exchange.
The dynamics of Br(2Pj) formation in the photodissociation of vinyl and perfluorovinyl bromides
Authors: Lee Kyoung-Seok , Lee Keon Woo , Kim Tae Kyu , Ryoo Ryong , Jung Kyung-Hoon
Published: May 2005

The photodissociation dynamics of vinyl bromide and perfluorovinyl bromide have been investigated at 234 nm using a photofragment ion imaging technique coupled with a state-selective [2+1] resonance-enhanced multiphoton ionization scheme. The nascent Br atoms stem from the primary C–Br bond dissociation leading to the formation of C2H3(X̃) and Br(2Pj;j=1/2,3/2). The obtained translational energy distributions have been well fitted by a single Boltzmann and three Gaussian functions. Boltzmann component has not been observed in the perfluorovinyl bromide. The repulsive A′3(n,σ*) state has been considered as the origin of the highest Gaussian components. Middle translational energy components with Gaussian shapes are produced from the A″1(π,σ*) and/or A″3(π,σ*) which are very close in energy. Low-energy Gaussian components are produced via predissociation from the A′1(π,π*) state. The assignments have also been supported by the recoil anisotropy corresponding to the individual components. It is suggested that intersystem crossing from the triplet states to the ground state has been attributed to the Boltzmann component and the fluorination reduces the probability of this electronic relaxation process.
Nuclear magnetic resonance and dielectric investigations of molecular motions in a glassy crystal: The mixed compound (CN-adm)0.75(Cl-adm)0.25
Authors: Decressain R. , Carpentier L. , Cochin E. , Descamps M.
Published: May 2005

The dynamic properties of plastic crystalline mixed adamantane’s derivatives namely cyanoadamantane (75%) and chloroadamantane (25%) were investigated by dielectric and nuclear magnetic resonance (NMR) spectroscopy, covering a spectral range of 12 decades in the temperature range 110–420 K. Phase transformations were studied and dynamical parameters of the plastic (I), glassy (Ig), and ordered (III) phases were determined and compared with those of pure compounds. The dynamics of the supercooled plastic phase is characterized by an α-process exhibiting an Arrhenius behavior which classified the mixed compound as a strong glass former. In the plastic phase, NMR relaxation times were interpreted by using a Frenkel model, which takes into account structural equilibrium positions. This model explains adequately the experimental results by considering two molecular motions. In both the glassy state and plastic phase the motional parameters agree with those of 1-cyanoadamantane. On the contrary, in the ordered phase, the motional parameters related to the uniaxial rotation of chloroadamantane molecules indicate an accelerated motion.
Vibrations in the B4 rhombic structure
Authors: Linguerri Roberto , Navizet Isabelle , Rosmus Pavel , Carter Stuart , Maier John P.
Published: May 2005

A double minimum six-dimensional potential energy surface (PES) is determined in symmetry coordinates for the most stable rhombic (D2h) B4 isomer in its Ag1 electronic ground state by fitting to energies calculated ab initio. The PES exhibits a barrier to the D4h square structure of 255 cm−1. The vibrational levels (J=0) are calculated variationally using an approach which involves the Watson kinetic energy operator expressed in normal coordinates. The pattern of about 65 vibrational levels up to 1600 cm−1 for all stable isotopomers is analyzed. Analogous to the inversion in ammonia-like molecules, the rhombus rearrangements lead to splittings of the vibrational levels. In B4 it is the B1g (D4h) mode which distorts the square molecule to its planar rhombic form. The anharmonic fundamental vibrational transitions of B411 are calculated to be (splittings in parentheses): G(0)=2352(22) cm−1, ν1(A1g)=1136(24) cm−1, ν2(B1g)=209(144) cm−1, ν3(B2g)=1198(19) cm−1, ν4(B2u)=271(24) cm−1, and ν5(Eu)=1030(166) cm−1 (D4h notation). Their variations in all stable isotopomers were investigated. Due to the presence of strong anharmonic resonances between the B1g in-plane distortion and the B2u out-of-plane bending modes, the higher overtones and combination levels are difficult to assign unequivocally.
Photoconductivity and current producing states in molecular semiconductors
Authors: Bittner Eric R. , Karabunarliev Stoyan , Ye Aijun
Published: May 2005

We present a methodology for computing photocurrent production in molecular semiconducting molecules. Our model combines a single-configuration interaction picture with the nonequilibrium Green’s function approach to compute the current response of a molecular semiconducting wire following excitation. We give detailed analysis of the essential excitonic, charge transfer, and dipole states for poly-(phenylenevinylene) chains of length 32 and 48 repeat units under an electric field bias and use this to develop a reduced dimensional tunneling model which accounts for chain-length and field-dependent behavior. In this paper, we consider the decay of an excited electron/hole state on a molecular wire under bias attached to semiconducting leads at either end. We find that the current produced by the decay of an excitation depends not only upon the lifetime of the state, as given by the imaginary part of its complex eigenvalue, but also upon the net charge on terminal ends of the molecule. We also find that weakly bound electron/hole charge-transfer pairs can decay into the continuum via field induced tunneling and produce a net current whereas excitonic states decay via tunneling but give no net current contribution.
Efficient and accurate approximations to the molecular spin-orbit coupling operator and their use in molecular g-tensor calculations
Authors: Neese Frank
Published: May 2005

Approximations to the Breit-Pauli form of the spin-orbit coupling (SOC) operator are examined. The focus is on approximations that lead to an effective quasi-one-electron operator which leads to efficient property evaluations. In particular, the accurate spin-orbit mean-field (SOMF) method developed by Hess, Marian, Wahlgren, and Gropen is examined in detail. It is compared in detail with the “effective potential” spin-orbit operator commonly used in density functional theory (DFT) and which has been criticized for not including the spin-other orbit (SOO) contribution. Both operators contain identical one-electron and Coulomb terms since the SOO contribution to the Coulomb term vanishes exactly in the SOMF treatment. Since the DFT correlation functional only contributes negligibly to the SOC the only difference between the two operators is in the exchange part. In the SOMF approximation, the SOO part is equal to two times the spin-same orbit contribution. The DFT exchange contribution is of the wrong sign and numerically shown to be in error by a factor of 2–2.5 in magnitude. The simplest possible improvement in the DFT-SOC treatment [Veff(-2X)-SOC] is to multiply the exchange contribution to the Veff operator by −2. This is verified numerically in calculations of molecular g-tensors and one-electron SOC constants of atoms and ions. Four different ways of handling the computationally critical Coulomb part of the SOMF and Veff operators are discussed and implemented. The resolution of the identity approximation is virtually exact for the SOC with standard auxiliary basis sets which need to be slightly augmented by steep s functions for heavier elements. An almost as efficient seminumerical approximation is equally accurate. The effective nuclear charge model gives results within ∼10% (on average) of the SOMF treatment. The one-center approximation to the Coulomb and one-electron SOC terms leads to errors on the order of ∼5%. Small absolute errors are obtained for the one-center approximation to the exchange term which is consequently the method of choice [SOMF(1X)] for large molecules.
Comparative analysis of local spin definitions
Authors: Herrmann Carmen , Reiher Markus , Hess Bernd A.
Published: May 2005

This work provides a survey of the definition of electron spin as a local property and its dependence on several parameters in actual calculations. We analyze one-determinant wave functions constructed from Hartree-Fock and, in particular, from Kohn-Sham orbitals within the collinear approach to electron spin. The scalar total spin operators Ŝ2 and Ŝz are partitioned by projection operators, as introduced by Clark and Davidson, in order to obtain local spin operators ŜA⋅ŜB and ŜzA, respectively. To complement the work of Davidson and co-workers, we analyze some features of local spins which have not yet been discussed in sufficient depth. The dependence of local spin on the choice of basis set, density functional, and projector is studied. We also discuss the results of Ŝz partitioning and show that 〈ŜzA〉 values depend less on these parameters than 〈ŜA⋅ŜB〉 values. Furthermore, we demonstrate that for small organic test molecules, a partitioning of Ŝz with preorthogonalized Löwdin projectors yields nearly the same results as one obtains using atoms-in-molecules projectors. In addition, the physical significance of nonzero 〈ŜA⋅ŜB〉 values for closed-shell molecules is investigated. It is shown that due to this problem, 〈ŜA⋅ŜB〉 values are useful for calculations of relative spin values, but not for absolute local spins, where 〈ŜzA〉 values appear to be better suited.
High-resolution electron spin resonance spectroscopy of XeF• in solid argon. The hyperfine structure constants as a probe of relativistic effects in the chemical bonding properties of a heavy noble gas atom
Authors: Misochko Eugenii Ya. , Akimov Alexander V. , Goldschleger Ilya U. , Tyurin Danil A. , Laikov Dimitri N.
Published: May 2005

Xenon fluoride radicals were generated by solid-state chemical reactions of mobile fluorine atoms with xenon atoms trapped in Ar matrix. Highly resolved electron spin resonance spectra of XeF• were obtained in the temperature range of 5–25 K and the anisotropic hyperfine parameters were determined for magnetic nuclei F19, Xe129, and Xe131 using naturally occurring and isotopically enriched xenon. Signs of parallel and perpendicular hyperfine components were established from analysis of temperature changes in the spectra and from numerical solutions of the spin Hamiltonian for two nonequivalent magnetic nuclei. Thus, the complete set of components of hyperfine- and g-factor tensors of XeF• were obtained: F19 (Aiso=435, Adip=1249 MHz) and Xe129 (Aiso=−1340, Adip=−485 MHz); g∥=1.9822 and g⊥=2.0570. Comparison of the measured hyperfine parameters with those predicted by density-functional theory (DFT) calculations indicates, that relativistic DFT gives true electron spin distribution in the Σ+2 ground-state, whereas nonrelativistic theory underestimates dramatically the electron-nuclear contact Fermi interaction (Aiso) on the Xe atom. Analysis of the obtained magnetic-dipole interaction constants (Adip) shows that fluorine 2p and xenon 5p atomic orbitals make a major contribution to the spin density distribution in XeF•. Both relativistic and nonrelativistic calculations give close magnetic-dipole interaction constants, which are in agreement with the measured values. The other relativistic feature is considerable anisotropy of g-tensor, which results from spin–orbit interaction. The orbital contribution appears due to mixing of the ionic Π2 states with the Σ+2 ground state, and the spin–orbit interaction plays a significant role in the chemical bonding of XeF•.
There is no generalization of known formulas for mutually unbiased bases
Authors: Archer Claude
Published: May 2005

In a quantum system having a finite number N of orthogonal states, two orthonormal bases {ai} and {bj} are called mutually unbiased if all inner products ⟨ai∣bj⟩ have the same modulus 1∕N. This concept appears in several quantum information problems. The number of pairwise mutually unbiased bases is at most N+1 and various constructions of such N+1 bases have been found when N is a power of a prime number. We study families of formulas that generalize these constructions to arbitrary dimensions using finite rings. We then prove that there exists a set of N+1 mutually unbiased bases described by such formulas, if and only if N is a power of a prime number.
Inhomogeneous multiscale dynamics in harmonic lattices
Authors: Cubero David , Yaliraki Sophia N.
Published: May 2005

We use projection operators to address the coarse-grained multiscale problem in harmonic systems. Stochastic equations of motion for the coarse-grained variables, with an inhomogeneous level of coarse graining in both time and space, are presented. In contrast to previous approaches that typically start with thermodynamic averages, the key element of our approach is the use of a projection matrix chosen both for its physical appeal in analogy to mechanical stability theory and for its algebraic properties. We show that thermodynamic equilibrium can be recovered and obtain the fluctuation dissipation theorem a posteriori. All system-specific information can be computed from a series of feasible molecular dynamics simulations. We recover previous results in the literature and show how this approach can be used to extend the quasicontinuum approach and comment on implications for dissipative particle dynamics type of methods. Contrary to what is assumed in the latter models, the stochastic process of all coarse-grained variables is not necessarily Markovian, even though the variables are slow. Our approach is applicable to any system in which the coarse-grained regions are linear. As an example, we apply it to the dynamics of a single mesoscopic particle in the infinite one-dimensional harmonic chain.
Laser induced fluorescence and resonant two-photon ionization spectroscopy of jet-cooled 1-hydroxy-9,10-anthraquinone
Authors: Cho Sung Haeng , Huh Hyun , Kim Hyung Min , Kim Choong Ik , Kim Nam Joon , Kim Seong Keun
Published: May 2005

We carried out laser induced fluorescence and resonance enhanced two-color two-photon ionization spectroscopy of jet-cooled 1-hydroxy-9,10-anthraquinone (1-HAQ). The 0-0 band transition to the lowest electronically excited state was found to be at 461.98 nm (21 646 cm−1). A well-resolved vibronic structure was observed up to 1100 cm−1 above the 0-0 band, followed by a rather broad absorption band in the higher frequency region. Dispersed fluorescence spectra were also obtained. Single vibronic level emissions from the 0-0 band showed Stokes-shifted emission spectra. The peak at 2940 cm−1 to the red of the origin in the emission spectra was assigned as the OH stretching vibration in the ground state, whose combination bands with the C=O bending and stretching vibrations were also seen in the emission spectra. In contrast to the excitation spectrum, no significant vibronic activity was found for low frequency fundamental vibrations of the ground state in the emission spectrum. The spectral features of the fluorescence excitation and emission spectra indicate that a significant change takes place in the intramolecular hydrogen bonding structure upon transition to the excited state, such as often seen in the excited state proton (or hydrogen) transfer. We suggest that the electronically excited state of interest has a double minimum potential of the 9,10-quinone and the 1,10-quinone forms, the latter of which, the proton-transferred form of 1-HAQ, is lower in energy. On the other hand, ab initio calculations at the B3LYP/6-31G(d,p) level predicted that the electronic ground state has a single minimum potential distorted along the reaction coordinate of tautomerization. The 9,10-quinone form of 1-HAQ is the lowest energy structure in the ground state, with the 1,10-quinone form lying ∼5000 cm−1 above it. The intramolecular hydrogen bond of the 9,10-quinone was found to be unusually strong, with an estimated bond energy of ∼13 kcal/mol (∼4500 cm−1), probably due to the resonance-assisted nature of the hydrogen bonding involved.
Infrared-visible and visible-visible double resonance spectroscopy of 1-hydroxy-9,10-anthraquinone-(H2O)n (n=1,2) complexes
Authors: Cho Sung Haeng , Huh Hyun , Kim Hyung Min , Kim Nam Joon , Kim Seong Keun
Published: May 2005

The structures of hydrated 1-hydroxyanthraquinone complexes (1-HAQ), 1-HAQ(H2O)n=1,2, with intramolecular and intermolecular hydrogen bonding interactions were studied using laser spectroscopic methods such as laser induced fluorescence, fluorescence-detected infrared, infrared-visible hole burning, and visible-visible hole burning spectroscopy. In the 1:1 complex 1-HAQ(H2O)1, the water binds to the free carbonyl group of 1-HAQ not associated with intramolecular hydrogen bond. The second water in the 1:2 complex, 1-HAQ(H2O)2, binds to the first water of the 1:1 complex rather than other hydrogen bonding sites of 1-HAQ. A pair of two geometric isomers was produced in a supersonic jet for each of the 1:1 and 1:2 complexes. Both isomers of each complex have the same vibrational spectra in the region of the OH stretching vibration of water, but have different energies for the 0-0 band of vibronic transition due to the asymmetry of the two phenyl rings in 1-HAQ. The 0-0 bands for all four species of 1-HAQ(H2O)n=1,2 were unambiguously assigned by comparing with the results of ab initio calculations, which yielded the structures, vibrational frequencies, and relative energies of the frontier molecular orbitals.
Interpretation of conservative forces from Stokesian dynamic simulations of interfacial and confined colloids
Authors: Anekal Samartha G. , Bevan Michael A.
Published: May 2005

This paper presents Stokesian dynamics simulations of experiments involving one or two charged colloids near either a single charged wall or confined between parallel charged walls. Equilibrium particle-particle and particle-wall interactions are interpreted from dynamic particle trajectories in simulations involving (1) a single particle levitated above a wall, (2) two particles below a wall, and (3) two particles confined between two parallel walls. By specifying only repulsive electrostatic Derjaguin–Landau–Verwey–Overbeek (DLVO) potentials and including multibody hydrodynamics, we successfully recover expected potentials in some cases, while anomalous attraction is observed in other cases. Attraction inferred in the latter simulations displays quantitative agreement with literature measurements when particle dynamics are interpreted using reported analyses. Because anomalous attraction is reproduced in simulations using only electrostatic repulsive DLVO potentials, our results reveal the one-dimensional analyses to be invalid for configurations that are inherently multidimensional via multibody hydrodynamics. Parameters related to experimental sampling of particle dynamics are also found to be critical for obtaining accurate potentials. We explain the anomalous attraction in each experiment using effective potentials, which can be employed in an a priori fashion to assist the confident design of future experiments involving interfacial and confined colloids. Ultimately, our findings reveal the importance of dimensionality and multibody hydrodynamics for understanding nonequilibrium dynamics of colloids near surfaces.
Functionally relevant protein motions: Extracting basin-specific collective coordinates from molecular dynamics trajectories
Authors: Pan Patricia Wang , Dickson Russell J. , Gordon Heather L. , Rothstein Stuart M. , Tanaka Shigenori
Published: May 2005

Functionally relevant motion of proteins has been associated with a number of atoms moving in a concerted fashion along so-called “collective coordinates.” We present an approach to extract collective coordinates from conformations obtained from molecular dynamics simulations. The power of this technique for differentiating local structural fuctuations between classes of conformers obtained by clustering is illustrated by analyzing nanosecond-long trajectories for the response regulator protein Spo0F of Bacillus subtilis, generated both in vacuo and using an implicit-solvent representation. Conformational clustering is performed using automated histogram filtering of the inter-Cα distances. Orthogonal (varimax) rotation of the vectors obtained by principal component analysis of these interresidue distances for the members of individual clusters is key to the interpretation of collective coordinates dominating each conformational class. The rotated loadings plots isolate significant variation in interresidue distances, and these are associated with entire mobile secondary structure elements. From this we infer concerted motions of these structural elements. For the Spo0F simulations employing an implicit-solvent representation, collective coordinates obtained in this fashion are consistent with the location of the protein’s known active sites and experimentally determined mobile regions.
Structural and electronic properties of S-doped fullerene C58: Where is the S atom situated?
Authors: Yuan Ren Xiao , Yang Liu Zi
Published: May 2005

Structural and electronic properties of S-doped fullerene C58 were calculated systematically via Hartree–Fock self-consistent field (SCF) and density functional B3LYP levels of theory with 6-31G(d) basis set. The most stable C58S represents an open cage structure with a nine-member ring orifice, which provides a large hole for large atoms or small molecules to pass through into the cage. The most stable endohedral S@C58 has the S atom seated near the center of the C58 cage. The calculated highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps of the isomers lie in the range of 1.42–2.50 eV. The electron affinity and the ionization potential were also presented as an indicator of the kinetic stability. Our results may aid in the design of experimental methods for controlling the nature of fullerene cages (for example, doping, opening, and reclosing them).
Liquid-vapor equilibrium and surface tension of nonconformal molecular fluids
Authors: del Rı́o Fernando , Dı́az-Herrera Enrique , Ávalos Edgar , Alejandre José
Published: May 2005

Molecular dynamics simulations at constant temperature have been performed on the liquid-vapor interface for fluids characterized by a recently introduced three-parameter potential. This potential is a modification of the well-known spherical Kihara interaction and is termed approximate nonconformal (ANC). It has been used successfully to describe many real molecules in the gaseous phase. Besides the usual molecular energy and size, the ANC potential introduces a third parameter s, called softness, to measure the form of the potential profile. Study of these systems shows that their critical and interfacial properties follow very closely those of four selected substances: argon, methane, propane, and hexane. Deviations of the properties predicted from the experimental values are analyzed and their probable causes are determined. The critical properties of ANC fluids and their dependence on s are also obtained via first-order perturbation theory in the form of an augmented van der Waals model. Analysis of the results shows that ANC potential functions can be used as reliable effective interactions for real dense fluids.
Stability boundaries, percolation threshold, and two-phase coexistence for polydisperse fluids of adhesive colloidal particles
Authors: Fantoni Riccardo , Gazzillo Domenico , Giacometti Achille
Published: May 2005

We study the polydisperse Baxter model of sticky hard spheres (SHS) in the modified mean spherical approximation (mMSA). This closure is known to be the zero-order approximation C0 of the Percus-Yevick closure in a density expansion. The simplicity of the closure allows a full analytical study of the model. In particular we study stability boundaries, the percolation threshold, and the gas-liquid coexistence curves. Various possible subcases of the model are treated in details. Although the detailed behavior depends upon the particularly chosen case, we find that, in general, polydispersity inhibits instabilities, increases the extent of the nonpercolating phase, and diminishes the size of the gas-liquid coexistence region. We also consider the first-order improvement of the mMSA (C0) closure (C1) and compare the percolation and gas-liquid boundaries for the one-component system with recent Monte Carlo simulations. Our results provide a qualitative understanding of the effect of polydispersity on SHS models and are expected to shed new light on the applicability of SHS models for colloidal mixtures.
Calculating intensities using effective Hamiltonians in terms of Coriolis-adapted normal modes
Authors: Karthikeyan S. , Krishnan Mangala Sunder , Carrington Tucker
Published: May 2005

The calculation of rovibrational transition energies and intensities is often hampered by the fact that vibrational states are strongly coupled by Coriolis terms. Because it invalidates the use of perturbation theory for the purpose of decoupling these states, the coupling makes it difficult to analyze spectra and to extract information from them. One either ignores the problem and hopes that the effect of the coupling is minimal or one is forced to diagonalize effective rovibrational matrices (rather than diagonalizing effective rotational matrices). In this paper we apply a procedure, based on a quantum mechanical canonical transformation for deriving decoupled effective rotational Hamiltonians. In previous papers we have used this technique to compute energy levels. In this paper we show that it can also be applied to determine intensities. The ideas are applied to the ethylene molecule.
Quantum mode-coupling theory for binary mixtures
Authors: Rabani Eran , Miyazaki Kunimasa , Reichman David R.
Published: May 2005

We extend the quantum mode-coupling theory of neat liquids to the case of binary mixtures, in order to study supercooled liquids where quantum fluctuations may compete with thermal fluctuations. We apply the theory to a generic model of a binary mixture of Lennard-Jones particles. Our treatment may be used to study quantum aging and exotic glass melting scenarios in structural supercooled quantum liquids.
Competition between adiabatic and nonadiabatic fragmentation pathways in the unimolecular decay of the ArI2(B) van der Waals complex
Authors: Roncero Octavio , Buchachenko Alexei A. , Lepetit Bruno
Published: May 2005

The competition between vibrational and electronic predissociations of the ArI2(B) van der Waals complex has been studied using several dynamical computational methods: exact quantum wave-packet propagation, time-dependent golden rule, and quasiclassical trajectory with quantum jumps model. Five electronic states are considered using recent three-dimensional coupled surfaces obtained with a perturbative diatoms-in-molecules method. Final vibrational and electronic populations, predissociation rates, and absorption spectra have been computed for I2(B,v=18–24)←I2(X,v=0) excitations within the complex. The contribution of vibrational predissociation into the total decay oscillates as a function of vibrational excitation due to intramolecular vibrational relaxation in a sparse-intermediate regime, which induces irregular variations of the total decay rate. Franck–Condon oscillations control the branching ratios of the individual electronic predissociation channels. However, since these oscillations are out of phase as a function of vibrational excitation, they have limited effect on the oscillatory behavior of the total predissociation rate. Comparison between exact quantum and perturbative golden rule calculations shows that vibrational predissociation has some impact on the electronic predissociation process and affects the final electronic distributions. On the contrary, vibrational product distributions are not significantly affected by the electronic predissociation. A classical description of the ArI2 dynamics provides an averaged picture of the competing predissociation processes, being better adapted for treating intermolecular vibrational relaxation in the statistical limit.
Distant-dipole field in liquids and diffusion: A perturbative approach
Authors: Engelsberg M. , Barros Wilson
Published: May 2005

A perturbative approach is employed to solve the Bloch-Torrey equations in the presence of distant-dipole fields in nuclear magnetic resonance. The procedure, although only carried out to first order in the perturbation parameter a=1/k2Dτd, could, in principle, be generalized to higher orders. Here D is the diffusivity, τd the dipolar demagnetization time, and k is the wave vector of the spatial modulation of magnetization produced by the magnetic field gradient. The results are especially interesting for dilute binary mixtures consisting of molecular species with different diffusivities. In this case the calculated two-dimensional correlation spectroscopy revamped by asymmetric Z-gradient echo detection spectra are shown to be free from some inadequacies resulting from a simplistic application of standard approximations.
Ab initio molecular dynamics simulation of liquid Al88Si12 alloys
Authors: Wang Songyou , Wang C. Z. , Chuang Feng-Chuan , Morris James R. , Ho K. M.
Published: May 2005

First-principles molecular dynamics simulations are carried out to study the structures, dynamics, and electronic properties of liquid Al88Si12 in the temperature ranging from 898 to 1298 K. The temperature dependence of static structure factors, pair correlation functions, and electronic density-of-states are investigated. The structural properties obtained from the simulations are in good agreement with the x-ray diffraction experimental results.
Structures and dynamics of thermosensitive microgel suspensions studied with three-dimensional cross-correlated light scattering
Authors: Pyett Stacy , Richtering Walter
Published: May 2005

The structure factors, short- and long-time diffusion coefficients, and hydrodynamic interactions of concentrated poly(N-isopropylacryamide) microgel suspensions were measured with simultaneous static and dynamic three-dimensional cross-correlated light scattering. The data are interpreted through comparison to hard sphere theory. The structure factors are known to be described well by the hard sphere approximation. When the structure factor is fit to an effective hard sphere volume fraction and radius, the diffusion and hydrodynamic interactions are also well described by the hard sphere model. We demonstrate that one single hard sphere volume fraction is sufficient to describe the microgel structures, hydrodynamic interactions, and long- and short-time collective diffusion coefficients. This result is surprising because the particle form of the microgels at these temperatures is not rigid, but rather “fuzzy” spheres with dangling polymer chains.
Optical and structural modeling of disclination lattices in carbonaceous mesophases
Authors: Gupta Gaurav , Hwang Dae Kun , Rey Alejandro D.
Published: May 2005

An integrated microstructural and optical model for carbonaceous mesophases is developed and used to explain the principles that govern the formation and stability of experimentally observed disclination lattices. The model is able to capture the orientation features of disclination lattices, including the type and location of disclination lines, and the orientation field in the mesophase matrix. The optical model based on reflection polarized optical microscopy is able to replicate all the details observed in actual observations. The typical brush figures have the proper distribution, orientation, and intensity. The computational predictions offer science-based routes to create and control desirable material architectures based on carbonaceous mesophase-carbon fiber composites.
The gap between crystalline and osmotic swelling of Na-montmorillonite: A Monte Carlo study
Authors: Meleshyn Artur , Bunnenberg Claus
Published: May 2005

Although the swelling of clay during moistening is a broadly experienced occurrence, the mechanisms driving it and especially the reason for the existence of a peculiar gap between crystalline and osmotic swelling of Na-montmorillonite are not yet fully understood. We obtained a deeper insight by means of Monte Carlo simulations of Na-montmorillonite swelling, which yield the swelling curve, interaction energies between and characteristic positions of structural atoms and water molecules. We find that a chainlike structure consisting of Na cations, water molecules, and oxygens of substituted tetrahedrons of neighboring mineral layers is formed in the interlayer space of Na-montmorillonite at a layer spacing of ∼19 Å, where experimental investigations show termination of crystalline swelling. Such a persistent structure may lock the interlayer space, until excess water is able to break this chain by osmotic forces. We suggest that its formation is the reason for the existence of a gap in layer spacings between ∼19 and ∼40 Å, which have been named “forbidden” layer spacings in experimental studies.
Calculation of nonadiabatic couplings in density-functional theory
Authors: Billeter Salomon R. , Curioni Alessandro
Published: May 2005

This paper proposes methods for calculating the derivative couplings between adiabatic states in density-functional theory (DFT) and compares them with each other and with multiconfigurational self-consistent field calculations. They are shown to be accurate and, as expected, the costs of their calculation scale more favorably with system size than post-Hartree-Fock calculations. The proposed methods are based on single-particle excitations and the associated Slater transition-state densities to overcome the problem of the unavailability of multielectron states in DFT which precludes a straightforward calculation of the matrix elements of the nuclear gradient operator. An iterative scheme employing linear-response theory was found to offer the best trade-off between accuracy and efficiency. The algorithms presented here have been implemented for doublet-doublet excitations within a plane-wave-basis and pseudopotential framework but are easily generalizable to other excitations and basis sets. Owing to their fundamental importance in cases where the Born-Oppenheimer separation of motions is not valid, these derivative couplings can facilitate, for example, the treatment of nonadiabatic charge transfers, of electron-phonon couplings, and of radiationless electronic transitions in DFT.
Observation of the lead carbonyls, PbnCO (n=1–4): Reactions of lead atoms and small clusters with carbon monoxide in solid argon
Authors: Jiang Ling , Xu Qiang
Published: May 2005

Reactions of laser-ablated Pb atoms with CO molecules in solid argon lead to the formation of the lead carbonyls, PbnCO (n=1–4), using matrix-isolation infrared spectroscopy. Absorption at 2027.7 cm−1 is assigned to C–O stretching mode of the PbCO product, which appears and increases on annealing, disappears on broadband irradiation, and recovers on further annealing. Small lead cluster mono-carbonyls PbnCO (n=2–4) are also observed in the present infrared spectra. Based on the results of stepwise annealing and the comparison with theoretical predictions, the absorptions at 1915.5, 1923.8, and 2042.8 cm−1 are assigned to Pb2CO, Pb3CO, and Pb4CO, respectively. Bridging CO is found in Pb2CO or Pb3CO, whereas terminal CO in Pb4CO. The density functional theory calculations have been performed on these molecules and small naked lead clusters. The good agreement between experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts provides strong support for the identifications of these lead mono-carbonyls PbnCO (n=1–4). Furthermore, energetic analysis for the possible reactions of lead atoms with CO molecules is also given.
Vibration-rotation interactions between overtone and combination levels of asymmetric-top molecules: Application to the infrared spectroscopy of formaldehyde and ketene
Authors: Smith David M.
Published: May 2005

The conventional vibration-rotation Hamiltonian for an asymmetric-top molecule is rewritten by expanding the elements of the inverse inertial tensor about the equilibrium molecular geometry. The approach allows the identification of terms in the Hamiltonian that couple states differing by two, three, or four vibrational quanta and hence the calculation of dimensioned Coriolis ξ coupling coefficients for interacting fundamental, overtone, and combination levels. The matrix elements that result from the application of the expanded Hamiltonian depend upon the harmonic vibrational wave numbers, equilibrium moments of inertia, Coriolis ζ parameters, and the derivatives of the elements of the inertial tensor matrix with respect to each of the normal coordinates. The Coriolis coupling coefficients may be calculated through evaluation of the summations that result from the appropriate terms. The validity of the approach is demonstrated through the calculation of coupling coefficients for interacting levels in formaldehyde and ketene. The uncertainty in the calculated values of the coupling coefficients is typically better than ±6%, although the values calculated for interactions that involve low-frequency vibrational modes are less reliable. Comparisons are made between the calculated values and experimental results.
Casimir energy in a conical wedge and a conical cavity
Authors: Ahmedov H. , Duru I. H.
Published: May 2005

Casimir energies for a massless scalar field for a conical wedge and a conical cavity are calculated. The group generated by the images is employed in deriving the Green function as well as the wave functions and the energy spectrum.
Perturbative and nonperturbative master equations for open quantum systems
Authors: Zhu Wusheng , Rabitz Herschel
Published: May 2005

This paper develops perturbative and nonperturbative master equations for open quantum systems based on time-dependent variational functionals. The perturbative equations are more concise and suitable for dealing with cases of weak system-environment coupling for short evolution time scales. The nonperturbative equations are valid for all time and appropriate to treat cases of strong system-environment coupling. When a system contains an external control field, both the perturbative and nonperturbative master equations reveal the embedded control field dependence upon the system decoherence, which provides a basis for decoherence management.
A revised model for diffusion induced segregation processes
Authors: Blesgen T.
Published: May 2005

A mathematical model for chalcopyrite disease within sphalerite is developed. As one main result, by analyzing the system enthalpy, correct expressions for the reaction terms in a system undergoing phase transitions are worked out. For the resulting equations, the thermodynamical validity is shown and the existence of a unique solution is proved.
Local and nonlocal symmetries for nonlinear telegraph equation
Authors: Bluman G. W. , Temuerchaolu  , Sahadevan R.
Published: May 2005

In this paper, local and nonlocal symmetry classifications are considered for four equivalent nonlinear telegraph equations. A complete potential symmetry classification of a scalar nonlinear telegraph equation is given through the point symmetry classification of a related potential system. Six new classes of equations are shown to admit potential symmetries. The relationships between local (including contact) and nonlocal (potential) symmetries of these equations are explored. A physical example is considered for possible applications of the obtained potential symmetries.
SCD patterns have singular diffraction
Authors: Baake M. , Frettlöh D.
Published: May 2005

Among the many families of nonperiodic tilings known so far, SCD tilings are still a bit mysterious. Here, we determine the diffraction spectra of point sets derived from SCD tilings and show that they have no absolutely continuous part, that they have a uniformly discrete pure point part on the axis Re3, and that they are otherwise supported on a set of concentric cylinder surfaces around this axis. For SCD tilings with additional properties, more detailed results are given.
The state dependence of the dynamic interactions in nanostructured particulate systems
Authors: Cimpoesu Dorin , Spinu Leonard , Stancu Alexandru
Published: May 2005

This paper is dedicated to the micromagnetic study of the temperature dependence of interactions in samples increasingly structured, with the standard deviations of the volume and orientation distributions becoming smaller and smaller. We have used the stochastic Landau–Lifshitz–Gilbert equation, observed the evolution of the interaction field distribution as a function of temperature during a number of magnetization processes and analyzed separately the contributions of the superparamagnetic and blocked particles.
Ab initio-based intermolecular carbon–carbon pair potentials for polycyclic aromatic hydrocarbon clusters
Authors: Lee Nam Ki , Kim Seong Keun
Published: May 2005

We derived the carbon–carbon pair potentials for polycyclic aromatic hydrocarbon (PAH) clusters, which exhibited a strikingly similar geometry to that of the two-layer graphite. The binding energy of PAH clusters ranging in size from the benzene dimer to the pyrene dimer obtained by ab initio calculations at the MP2 level was used to extract the pair potentials in the form of the Lennard-Jones and Exponential-6 functions. Identical binding energy and equilibrium interlayer distance were reproduced by these functions to those calculated by the ab initio method. The pair potentials for PAHs yield the same equilibrium C–C distance as the known pair potentials for graphite and fullerenes, but nearly twice the well depth because of the polarization of the C–H bond.
Structural and magnetic properties of monolayer film of CoPt nanoparticles synthesized by polyol process
Authors: Mizuno M. , Sasaki Y. , Inoue M. , Chinnasamy C. N. , Jeyadevan B. , Hasegawa D. , Ogawa T. , Takahashi M. , Tohji K. , Sato K. , Hisano S.
Published: May 2005

Co 43 Pt 57 nanoparticle dispersion was synthesized by using the polyol process, and monolayer film of the particles with [3-(2-aminoethylamino)propyl]trimethoxysilane coupling layer on a silicon substrate was fabricated and characterized. After the film was annealed at 873K, the Co43Pt57 nanoparticles transformed from their as-deposited fcc phase to L10 structure. However, the resulting c∕a ratio was only 0.993, indicating incomplete transformation. Grain size of the annealed film was 4.9nm against 4.1nm for the as-deposited state. The annealed film showed the presence of high anisotropic phase with the remanence coercivity of 4.2kOe and anisotropy field over 25kOe at RT.