bluuebunny/crossref_metadata_2025 huggingface dataset:
The structure of the second-order reduced density matrix in density matrix functional theory and its construction from formal criteria
Authors: Kollmar Christian , Heß Bernd A.
Published: February 2004

Some formal requirements for the second-order reduced density matrix are discussed in the context of density matrix functional theory. They serve as a basis for the ad hoc construction of the second-order reduced density matrix in terms of the first-order reduced density matrix and lead to implicit functionals where the occupation numbers of the natural orbitals are obtained as diagonal elements of an idempotent matrix the elements of which represent the variational parameters to be optimized. The numerical results obtained from a first realization of such an implicit density matrix functional give excellent agreement with the results of full configuration interaction calculations for four-electron systems like LiH and Be. Results for H2O taken as an example for a somewhat larger molecule are numerically less satisfactory but still give reasonable occupation numbers of the natural orbitals and indicate the capability of density matrix functional theory to cope with static electron correlation.
Vibrational zero-point energies and thermodynamic functions beyond the harmonic approximation
Authors: Barone Vincenzo
Published: February 2004

This paper compares harmonic and anharmonic zero-point energies and thermodynamic functions for a number of molecules of small and medium size. Anharmonic corrections cannot be neglected for quantitative studies, but can be obtained quite effectively by a perturbative treatment including cubic force constants to the second order and semidiagonal quartic constants to the first order. Simple finite difference equations provide all the necessary terms by at most 6N-11 Hessian evaluations, where N is the number of atoms in the system. Accurate values are obtained by this method using the Becke three parameter Lee–Yang–Parr functional, medium size basis sets, and, when needed, proper treatment of internal rotations. The whole model has been completely automated in the Gaussian package.
An algorithm for large scale density matrix renormalization group calculations
Authors: Chan Garnet Kin-Lic
Published: February 2004

We describe in detail our high-performance density matrix renormalization group (DMRG) algorithm for solving the electronic Schrödinger equation. We illustrate the linear scalability of our algorithm with calculations on up to 64 processors. The use of massively parallel machines in conjunction with our algorithm considerably extends the range of applicability of the DMRG in quantum chemistry.
Ornstein–Uhlenbeck diffusion quantum Monte Carlo study on the bond lengths and harmonic frequencies of some first-row diatomic molecules
Authors: Lu Shih-I
Published: February 2004

This article accesses the performance of the Ornstein–Uhlenbeck diffusion quantum Monte Carlo with regard to the calculation of molecular geometries and harmonic frequencies of H2, LiH, HF, Li2, LiF, CO, N2, and F2 molecules. A comparison of the results for the eight first-row diatomic molecules from experiments, CCSD(T)/6-311G(3df,3pd) and CCSD(T)/cc-pV5Z levels of theory as well as our work is given. The results presented show that quantum Monte Carlo is becoming powerful tools for ab initio electronic structure calculations.
Cooperative radiative and nonradiative effects in K2NaScF6 codoped with V3+ and Er3+
Authors: Reinhard Christine , Krämer Karl , Biner Daniel A. , Güdel Hans U.
Published: February 2004

K 2 NaScF 6 crystals codoped with V3+ and Er3+ exhibit some novel cooperative near-IR to visible upconversion processes at cryogenic temperatures. V3+ mainly acts as a broadband sensitizer. The V3+ 3T1g→3T2g excitation between 13 500 and 15 500 cm−1, after fast relaxation to V3+ 1T2g, can be transferred to Er3+ 4I11/2, and then upconversion takes place. Four upconversion mechanisms are identified and characterized. For narrow-band laser excitation the overall efficiency of the upconversion processes is low. However, at 12 K for broadband excitation, such as in a lamp, between 12 000 and 14 500 cm−1 the number of emitted visible photons is roughly doubled by codoping V3+ in addition to Er3+.
Fluorescence intensities of chromophores in front of a thin metal film
Authors: Vasilev Krasimir , Knoll Wolfgang , Kreiter Maximilian
Published: February 2004

The fluorescence intensity from a planar multilayered system with a chromophore separated from a gold film by a dielectric spacer is measured quantitatively. The direction of excitation and the spacer thickness are varied and the angular distribution of the emission is recorded as well as its polarization. The experimental data are compared to the predictions obtained from classical electromagnetic theory, taking into account the refractive indices of the layer system as well as the nonradiative decay rate and the relative orientation of absorption and emission dipole moments of the dye. Excellent agreement is found for a spacer thickness above 15 nm if proper values for these parameters are used. Samples with thinner spacer layers show significant deviations from classical theory.
The efficiency of photolyase and indole complexes to repair DNA containing dimers of pyrimidine: A theoretical analysis of the electron transfer reactions
Authors: Volcov Flávia , Goldman Carla
Published: February 2004

We analyze the effects of competing reactions to the efficiency of enzymatic splitting of pyrimidine dimers formed in DNA by the incidence of ultraviolet radiation. This is accomplished with the aid of a formula that expresses the efficiency of the repair in terms of parameters that regulate the reaction rates for primary and for back long-range electron transfers taking place in the process. Comparison of experimental data with estimations on account of this formula supports early conjectures in the literature that attribute the relative high performance of the enzymatic complexes of photolyase to its ability to suppress the back reaction.
Melting behavior of one-dimensional zirconium nanowire
Authors: Hui Li , Wang B. L. , Wang J. L. , Wang G. H.
Published: February 2004

In this paper, we analyze the melting behavior of zirconium nanowire using the results of a series of molecular dynamics simulations. Our calculation employs a well-fitted, tight-binding many-body potential for zirconium atoms. The melting point of the nanowire is predicted by the root-mean-square displacements for inner and outer shells. Our simulations predict two melting behaviors: one is the inner melting and the other is the outer melting. Our results reveal that the melting of nanowire starts from the inner shell atoms. The melting point of zirconium nanowire is lower than the bulk value (2125 K). Moreover, the melting point of the inner shell is lower than that of the outer shell. A coexistence of crystal and liquid units is observed in the melting process of nanowire. An investigation of local clusters is carried out to further analyze the melting mechanism of the nanowire. The presence of the local clusters 1331, 1321, 1211, etc. is an indication of disordered structures. The pair and angular correlation functions are also presented for the analysis of the melting behavior. It is not only the diffusion of single atom but the diffusion of clusters result in the occurrence of the melting.
Intersections of potential energy surfaces of short-lived states: The complex analogue of conical intersections
Authors: Feuerbacher Sven , Sommerfeld Thomas , Cederbaum Lorenz S.
Published: February 2004

Whereas conical intersections between potential energy surfaces of bound states are well known, the interaction of short-lived states has been investigated only rarely. Here, we present several systematically constructed model Hamiltonians to study the topology of intersecting complex potential energy surfaces describing short-lived states: We find the general phenomenon of doubly intersecting complex energy surfaces, i.e., there are two points instead of one as in the case of bound states where the potential energy surfaces coalesce. In addition, seams of intersections of the respective real and imaginary parts of the potential energy surfaces emanate from these two points. Using the Σ* and Π* resonance states of the chloroethene anion as a practical example, we demonstrate that our complete linear model Hamiltonian is able to reproduce all phenomena found in explicitly calculated ab initio complex potential energy surfaces.
Fourier transform millimeter-wave spectroscopy of the ethyl radical in the electronic ground state
Authors: Kim Eunsook , Yamamoto Satoshi
Published: February 2004

The pure rotational spectrum of the ethyl radical (C2H5) has been detected for the first time with the Fourier transform millimeter-wave spectrometer. The ethyl radical is produced by discharging the C2H5I gas diluted in Ar. The 101–000 rotational transition of the ethyl radical is observed in the frequency range from 43 680 to 43 780 MHz. The observed spectrum shows a very complicated pattern of the fine and hyperfine structures of a doublet radical with the nuclear spins of five protons. The fine and hyperfine components are assigned with the aid of measurements of the Zeeman splittings. As a result, the 22 lines are ascribed to the transitions in the ground vibronic state (A2″). The rotational constant, the spin–rotation interaction constant, and hyperfine interaction constants are determined by the least-squares fit. The Fermi contact term of the α-proton is determined to be −64.1654 MHz in the gas phase, indicating that the structure of the -CH2 is essentially planar. The present rotational spectroscopic study further supports that the methyl group of the ethyl radical can be regarded as a nearly free internal rotor with a low energy barrier. A few unassigned lines still remain, which may be vibrational satellites of the internal rotation mode.
A coarse-grained model and associated lattice Monte Carlo simulation of the coil–helix transition of a homopolypeptide
Authors: Chen Yantao , Zhang Qi , Ding Jiandong
Published: February 2004

A new coarse-grained lattice model neglecting atomic details is proposed for the coil–helix transition and a new physical parameter is suggested to characterize a helical structure. In our model, each residue is represented by eight lattice sites, and side groups are not considered explicitly. Chirality and hydrogen bonding are taken into consideration in addition to chain connectivity and the excluded volume effect. Through a dynamic Monte Carlo simulation, the physical properties of the coil–helix transition of a single homopolypeptide have been produced successfully within a short computing time on the PC. We also examined the effects of the variation of chain configurations including chain size and chain shape, etc. A spatial correlation function has been introduced in order to characterize periodicity of a helical chain in a simple way. A propagation parameter and a nucleation parameter have also been calculated, which compares favorably with the results of the Zimm–Bragg theory for the coil–helix transition.
Ab initio study on the spectroscopy of CuCl2. I. Benchmark calculations on the X 2Πg–2Σg+ transition
Authors: Ramı́rez-Solı́s A. , Daudey J. P.
Published: February 2004

The modern theoretical predictions on the ΛSΣ nature of the ground state of CuCl2 have led to different answers, depending on the type (DFT-based or ab initio) and the quality of the electronic correlation treatment; for this reason the X 2Πg–2Σg+ transition energy has been predicted to range from −1856 to +5887 cm−1. The physical problem at hand lies in the difficulty of accurately describing the orientation of the 3d hole on the central Cu2+(3d9)/Cu+(3d94s1) ion (in the field of both chlorine ions), which implies the need of the most sophisticated nondynamic and dynamic electronic correlation treatments. We report here ab initio benchmark calculations using especially developed basis sets to study, at the CASSCF+CASPT2 and CASSCF+ACPF levels, the transition energy as well as the corresponding equilibrium geometries. The spin–orbit (SO) effects of both atoms were included in a second step through the effective Hamiltonian formalism, using the calibrated SO effective potentials developed by the Stuttgart group. Without SO at the CASSCF+ACPF level, the ground state is X 2Πg but the vertical transition energy to the 2Σg+ is only 99 cm−1 at 3.95 a.u. The inclusion of the SO effects leads to a Ω=1/2 (59% 2Πg,41% 2Σg+) ground state, in contradiction with the Ω experimental value of 3/2. In a last step we show that the SO effects (and therefore the final Ω ordering) are critically dependent on the ΛSΣ electronic energies, so that it is not impossible that the Ω ordering is actually changed. For theoreticians interest in this matter is not purely academic, since many properties of organometallic complexes are linked to such delicate physical effects.
A molecular dynamics study of the dielectric properties of aqueous solutions of alanine and alanine dipeptide
Authors: Boresch Stefan , Willensdorfer Martin , Steinhauser Othmar
Published: February 2004

Molecular dynamics simulations were used to compute the frequency-dependent dielectric susceptibility of aqueous solutions of alanine and alanine dipeptide. We studied four alanine solutions, ranging in concentration from 0.13–0.55 mol/liter, and two solutions of alanine dipeptide (0.13 and 0.27 mol/liter). In accord with experiment we find a strong dielectric increment for both solutes, whose molecular origin is shown to be the zwitterionic nature of the solutes. The dynamic properties were analyzed based on a dielectric component analysis into solute, a first hydration shell, and all remaining (bulk) waters. The results of this three component decomposition were interpreted directly, as well as by uniting the solute and hydration shell component to a “suprasolute” component. In both approaches three contributions to the frequency-dependent dielectric properties can be discerned. The quantitatively largest and fastest component arises from bulk water [i.e., water not influenced by the solute(s)]. The interaction between waters surrounding the solute(s) (the hydration shell) and bulk water molecules leads to a relaxation process occurring on an intermediate time scale. The slowest relaxation process originates from the solute(s) and the interaction of the solute(s) with the first hydration shell and bulk water. The primary importance of the hydration shell is the exchange of shell and bulk waters; the self-contribution from bound water molecules is comparatively small. While in the alanine solutions the solute–water cross-terms are more important than the solute self-term, the solute contribution is larger in the dipeptide solutions. In the latter systems a much clearer separation of time scales between water and alanine dipeptide related properties is observed. The similarities and differences of the dielectric properties of the amino acid/peptide solutions studied in this work and of solutions of mono- and disaccharides and of the protein ubiquitin are discussed.
Direct observation of an isopolyhalomethane O–H insertion reaction with water: Picosecond time-resolved resonance Raman (ps-TR3) study of the isobromoform reaction with water to produce a CHBr2OH product
Authors: Kwok Wai Ming , Zhao Cunyuan , Li Yun-Liang , Guan Xiangguo , Phillips David Lee
Published: February 2004

Picosecond time-resolved resonance Raman (ps-TR3) spectroscopy was used to obtain the first definitive spectroscopic observation of an isopolyhalomethane O–H insertion reaction with water. The ps-TR3 spectra show that isobromoform is produced within several picoseconds after photolysis of CHBr3 and then reacts on the hundreds of picosecond time scale with water to produce a CHBr2OH reaction product. Photolysis of low concentrations of bromoform in aqueous solution resulted in noticeable formation of HBr strong acid. Ab initio calculations show that isobromoform can react with water to produce a CHBr2(OH) O–H insertion reaction product and a HBr leaving group. This is consistent with both the ps-TR3 experiments that observe the reaction of isobromoform with water to form a CHBr2(OH) product and photolysis experiments that show HBr acid formation. We briefly discuss the implications of these results for the phase dependent behavior of polyhalomethane photochemistry in the gas phase versus water solvated environments.
On the use of Bennett’s acceptance ratio method in multi-canonical-type simulations
Authors: Fenwick Michael K. , Escobedo Fernando A.
Published: February 2004

A common strategy for mapping coexistence curves is to employ multi-canonical (MUCA) sampling to simulate along a macrostate path connecting two phases. Central to this approach is the task of accurately calculating the importance weights used in the MUCA procedure, which are needed for both effective sampling and accurate determination of phase boundaries. The purpose of this study is to develop a strategy for determining the importance weights that is built upon Bennett’s optimized acceptance ratio method. This approach is shown to be closely related to transition matrix schemes, and is used to compute the vapor–liquid equilibrium of a Lennard-Jones fluid and the liquid–liquid equilibrium of a n-hexane/n-perfluorohexane mixture. For the Lennard-Jones system, the importance weights as a function of the number of particles “N” (at fixed temperature and volume) are obtained by using Bennett’s method to estimate free energy differences between N and N+1 particle systems over the desired range of N values. In this application, the method is found to perform slightly better than a related transition matrix scheme. For the n-hexane/n-perfluorohexane liquid mixture, the method is designed to obtain weights as a function of composition (for fixed temperature, pressure, and total number of particles); in this case, the method is found to outperform the Gibbs ensemble approach.
Ca
@
C
82
isomers: Computed temperature dependency of relative concentrations
Authors: Slanina Zdeněk , Kobayashi Kaoru , Nagase Shigeru
Published: February 2004

Relative concentrations of nine isomers of Ca@C82 derived from the C82 isolated-pentagon-rule satisfying cages are computed in a wide temperature interval. The computations are based on the Gibbs energy constructed from partition functions supplied with molecular parameters from density functional theory calculations. Five structures show significant populations at higher temperatures: C2v>Cs>C2>C3v>Cs. The computed relative stabilities agree well with available observations.
Detection of ClSO with time-resolved Fourier-transform infrared absorption spectroscopy
Authors: Chu Li-Kang , Lee Yuan-Pern , Jiang Eric Y.
Published: February 2004

ClSO was produced as an intermediate upon irradiating a flowing mixture of Cl2SO and Ar with a KrF excimer laser at 248 nm. A step-scan Fourier-transform infrared spectrometer coupled with a small multipass absorption cell was employed to detect time-resolved absorption spectrum of ClSO. A transient spectrum in the region 1120–1200 cm−1, which diminished on prolonged reaction, is assigned to the S–O stretching (ν1) mode of ClSO. A spectrum with a resolution of 0.3 cm−1 partially reveals rotational structure with the Q-branch at 1162.9 cm−1. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ) predict the geometry, vibrational, and rotational parameters of ClSO. An IR absorption spectrum of ClSO simulated based on predicted rotational parameters agrees satisfactorily with experimental results. ClSO produced from photolysis of Cl2SO at 248 nm is internally hot.
Disagreement between theory and experiment in the simplest chemical reaction: Collision energy dependent rotational distributions for H+D2→HD(ν′=3,j′)+D
Authors: Pomerantz Andrew E. , Ausfelder Florian , Zare Richard N. , Althorpe Stuart C. , Aoiz F. J. , Bañares Luis , Castillo Jesus F.
Published: February 2004

We present experimental rotational distributions for the reaction H+D2→HD(ν′=3,j′)+D at eight different collision energies between 1.49 and 1.85 eV. We combine a previous measurement of the state-resolved excitation function for this reaction [Ayers et al., J. Chem. Phys. 119, 4662 (2003)] with the current data to produce a map of the relative reactive cross section as a function of both collision energy and rotational quantum number (an E–j′ plot). To compare with the experimental data, we also present E–j′ plots resulting from both time-dependent and time-independent quantum mechanical calculations carried out on the BKMP2 surface. The two calculations agree well with each other, but they produce rotational distributions significantly colder than the experiment, with the difference being more pronounced at higher collision energies. Disagreement between theory and experiment might be regarded as surprising considering the simplicity of this system; potential causes of this discrepancy are discussed.
Collision energy dependence of the HD(ν′=2) product rotational distribution of the H+D2 reaction in the range 1.30–1.89 eV
Authors: Ausfelder Florian , Pomerantz Andrew E. , Zare Richard N. , Althorpe Stuart C. , Aoiz F. J. , Bañares Luis , Castillo Jesus F.
Published: February 2004

An experimental and theoretical investigation of the collision energy dependence of the HD(ν′=2,j′) rotational product state distribution for the H+D2 reaction in the collision energy range of Ecol=1.30–1.89 eV has been carried out. Theoretical results based on time-dependent and time-independent quantum mechanical methods agree nearly perfectly with each other, and the agreement with the experiment is good at low collision energies and very good at high collision energies. This behavior is in marked contrast to a previous report on the HD(ν′=3,j′) product state rotational distribution [Pomerantz et al., J. Chem. Phys. 120, 3244 (2004)] where a systematic difference between experiment and theory was observed, especially at the highest collision energies. The reason for this different behavior is not yet understood. In addition, this study employs Doppler-free spectroscopy to resolve an ambiguity in the E, F–X resonantly enhanced multiphoton ionization transition originating from the HD(ν′=2,j′=1) state, which is found to be caused by an accidental blending with the transition coming from the HD(ν′=1,j′=14) state.
Reassignment of the CH stretching frequency of CHF in the Ã electronic state
Authors: Nauta Klaas , Guss Joseph S. , Owens Nathan L. , Kable Scott H.
Published: February 2004

The 20 000–24 000 cm−1 region of the Ã(1A″)←X̃(1A′) transition of supersonically cooled fluoromethylene has been remeasured using laser induced fluorescence spectroscopy. Several new bands involving the ν1 (C–H stretching) vibrational frequency in the excited state are reported, allowing for the first time an accurate determination of ν1′=2799.7 cm−1 and x12′=−34.8 cm−1. The value of x22′ has been recalculated to be −7.4 cm−1. Dispersed fluorescence spectroscopy was used to confirm the identity of the ν1 vibrational bands. Several sequence bands involving the ν3 (C–F stretching) vibrational frequency are also reported.
Transient response of a Brownian particle with general damping
Authors: Chen L. Y. , Nash Patrick L.
Published: February 2004

We study the transient response of a Brownian particle with general damping in a system of metastable potential well. The escape rate is evaluated as a function of time after an infinite wall is removed from the potential barrier. It takes a relaxation time for the rate to reach its limit value and this rate relaxation time differs from the relaxation time of the majority of the probability around the bottom of the potential well. The rate relaxation time is found to depend on the temperature as well as the damping constant. It involves the diffusion time and the instanton time, in general agreement with recent studies of the overdamped case by Bier et al. [Phys. Rev. E 59, 6422 (1999)].
Polymer translocation through a nanopore. II. Excluded volume effect
Authors: Kong C. Y. , Muthukumar M.
Published: February 2004

Following our previous study of a Gaussian chain translocation, we have investigated the transport of a self-avoiding chain from one sphere to another sphere through a narrow pore, using the self-consistent field theory formalism. The free energy landscape for polymer translocation is significantly modified by excluded volume interactions among monomers. The free energy barrier for the placement of one of the chain ends at the pore depends on the chain length N nonmonotonically, in contrast to the N-independence for Gaussian chains. This results in a nonmonotonic dependence of the average arrival time 〈τ0〉 on N for self-avoiding chains. When the polymer chain is partitioned between the donor and recipient spheres, a local free energy minimum develops, depending on the strength w of the excluded volume interaction and the relative sizes of the donor and recipient spheres. If the sizes of spheres are comparable, the average translocation time 〈τ〉 (the average time taken by the polymer, after the arrival at the pore, to convert from the donor to the recipient) increases with an increase in w for a fixed N value. On the other hand, for the highly asymmetric sizes of the donor and recipient spheres, 〈τ〉 decreases with an increase in w. As in the case of Gaussian chains, 〈τ〉 depends nonmonotonically on the pore length.
Nonlinear rheological behavior associated with structural transitions in block copolymer solutions via nonequilibrium molecular dynamics
Authors: Rychkov Igor , Yoshikawa Kenichi
Published: February 2004

The nonequilibrium molecular dynamics computer simulation method was used to study microsegregated block copolymer systems in a selective solvent under a shear flow field. Two polymer concentrations were considered, 0.3 and 0.4, corresponding to the body centered cubic spherical and hexagonal cylindrical zero-shear phases, respectively. As the shear rate increased, both systems exhibited two-stage shear thinning, a peak in the scalar pressure, and normal stress differences. Microscopic connections were investigated by calculating the gyration and bond orientation tensors and the interaction energies per particle. At high shear rates, polymer chains elongate and orient along the direction of shear, and this is accompanied by the breaking-up of domains. The structure-rheology relation was discussed with regard to the morphological changes reported in our last study for the same systems. In particular, the structurally relevant critical values of the shear rate were found to delimit different behaviors of the shear rate-dependencies obtained in this work.
A continuum, O(N) Monte Carlo algorithm for charged particles
Authors: Rottler Jörg , Maggs A. C.
Published: February 2004

We introduce a Monte Carlo algorithm for the simulation of charged particles moving in the continuum. Electrostatic interactions are not instantaneous as in conventional approaches, but are mediated by a constrained, diffusing electric field on an interpolating lattice. We discuss the theoretical justifications of the algorithm and show that it efficiently equilibrates model electrolytes and polar fluids. In order to reduce lattice artifacts that arise from the interpolation of charges to the grid we implement a local, dynamic subtraction algorithm. This dynamic scheme is completely general and can also be used with other Coulomb codes, such as multigrid based methods.
Low-temperature adsorption of gases on metal surfaces (Review)
Authors: Ptushinskiı̆ Yu. G.
Published: February 2004

A review of the published results on the adsorption of some simple gases on metal surfaces at low substrate temperatures (Ts⩽30 K, down to liquid helium temperatures) is given. The methods of investigating low-temperature adsorption of gases are briefly discussed. Attention is focused primarily on the adsorption of hydrogen on transition metals and noble metals. The results of experimental studies on transition metals include information about the state of the adsorbed particles (atoms or molecules), the spectra of the adsorption states, the kinetics of adsorption–desorption processes, the participation of precursor states in the adsorption mechanism, the role of various quantum properties of the H2 and D2 molecules, the influence of two-dimensional phase transitions, the structure of the adsorbed layer (adlayer), and electron-stimulated processes. Experimental studies of the adsorption of hydrogen on noble metals in conjunction with theoretical calculations provide information about the fine details of the quantum sticking mechanism, in particular, the trapping of molecules into quasi-bound states and the influence of diffraction by the lattice of surface atoms. Data on the role of the rotational state of the molecules, ortho–para conversion, and direct photodesorption are examined. A review of the relatively few papers on the adsorption of oxygen, carbon monoxide, and nitrogen is also given.
Size effect in the desorption of excited atoms and molecules from clusters of inert elements under electron bombardment
Authors: Verkhovtseva É. T. , Bondarenko E. A. , Doronin Yu. S.
Published: February 2004

New channels of desorption of excited atoms and molecules from clusters of argon, krypton, and xenon under electron bombardment are found by the method of vacuum ultraviolet emission spectroscopy. The maximum yield of particles is registered in the interval of average sizes of 50–100 atoms/cluster. The regularities and features of the desorption of excited particles are revealed, making it possible to establish a new desorption mechanism called nonradiative excimeric dissociation. It is shown that the main stages of this mechanism are: the formation of molecular centers of the nature of highly excited diatomic excimer molecules in clusters in the process of self-trapping of high-energy p excitons (n=1); the nonradiative dissociation of these molecules to excited atoms and atoms in the ground state with large kinetic energies. It is established that the appearance of new channels of desorption of excited atoms and molecules from clusters under bombardment by electrons is due to features of the physical properties of clusters in the interval of average sizes 50–100 atoms/cluster, in particular, to features of the energy spectrum, vibrational frequency spectrum of the atoms, and exciton energy relaxation.
Stationary nonlinear waves at the surface of a thin liquid layer under inverted gravitation conditions
Authors: Kolmakov G. V. , Lebedeva E. V. , Levchenko A. A. , Mezhov-Deglin L. P. , Trusov A. B. , Shikin V. B.
Published: February 2004

Instability of the flat surface of a thin liquid layer wetting a solid substrate under inverted gravitation conditions is discovered. The development of this instability leads to the formation of a new stationary nonuniform liquid surface state. It looks like a solitary hill with characteristics sensitive to the liquid film parameters, particularly to the layer thickness at which the instability begins to develop. By application of a variational approach the mechanical stability of such a hill (droplet) in the one-dimensional approximation is proved. A variational picture of the shape evolution for a cylindrical charged droplet in an external electric field is constructed, too. The results obtained are compared with an experiment on liquid hydrogen droplets [A. A. Levchenko, G. V. Kolmakov, L. P. Mezhov-Deglin, M. G. Mikhailov, and A. B. Trusov, Low Temp. Phys. 25, 242 (1999)]. The theory developed is in good agreement with the results of experiments.
Quantum Monte Carlo for electronic excitations of free-base porphyrin
Authors: Aspuru-Guzik Alán , El Akramine Ouafae , Grossman Jeffrey C. , Lester William A.
Published: February 2004

Accurate calculations of allowed and nonallowed transitions in porphyrin are reported. Using the quantum Monte Carlo method in the diffusion Monte Carlo variant, the vertical transition between the ground state singlet and the second excited state singlet as well as the adiabatic transition between the ground state and the lowest triplet state have been computed for this 162-electron system. The present theoretical results are compared to experiment and to results of other theoretical methods. The diffusion Monte Carlo energy differences are found to be in excellent agreement with experiment.
Relativistic Kinetic Equations Including Radiation Effects. I. Vlasov Approximation
Authors: Hakim Rémi , Mangeney André
Published: February 2004

In a preceding series of papers, we developed relativistic statistical mechanics of electromagnetically interacting particles. Here we derive a hierarchy of manifestly covariant equations for the reduced densities. This hierarchy is valid at order one in a parameter which is closely related to radiation phenomena. At the lowest order (absence of correlation between particles), we derive a kinetic equation which is a modification of the relativistic Vlasov equation. The added term introduces the effects of the emission of collective radiation. A dimensional analysis shows that this term is important when mc2 ∼ kT, i.e., when the plasma is relativistic. The modified Vlasov equation is shown to be irreversible: an H theorem is proved. Several applications are studied: dispersion relations, hydrodynamical equations. We have also discussed the Einstein-Ritz controversy on the connection between retarded actions and irreversibility.
Cluster Expansions in Many-Fermion Theory. I. ``Factor-Cluster'' Formalisms
Authors: Clark John W. , Westhaus Paul
Published: February 2004

Cluster development may furnish a powerful device for the calculation of the expectation values of the observables of a many-fermion system with respect to dynamically correlated state vectors. The generalized normalization integral, a generating function for the required expectation values, is defined, and four of the many possible decompositions of this function into cluster integrals are explored. Two of these decompositions are slight extensions of the conventional ones of Iwamoto and Yamada and Aviles, Hartogh, and Tolhoek. The other two are product decompositions, leading to new ``factor-cluster'' formalisms. A factor-cluster expansion is applied to the evaluation of the n-particle spatial distribution function.
Cluster Expansions in Many-Fermion Theory. II. Rearrangements of Primitive Decomposition Equations
Authors: Westhaus Paul , Clark John W.
Published: February 2004

The ``factor-cluster'' formalisms introduced in the preceding paper are used as a tool for a further development of the cluster theories proposed by Iwamoto and Yamada and by Aviles, Hartogh, and Tolhoek. The primitive decomposition characterizing each of the older formalisms is rearranged into the exponential of a series with a uniform N dependence in the limit of large N. In addition a ``linked cluster'' theorem is proven for the series comprising the exponent in the Iwamoto-Yamada formalism. Our derivations, unlike those of earlier authors, are valid for all N.
Reduction of Relativistic Wavefunctions to the Irreducible Representations of the Inhomogeneous Lorentz Group. Part II. Zero-Mass Components
Authors: Moses H. E.
Published: February 2004

In a previous paper, we showed how wavefunctions which transform in a relativistic manner in configuration space can be expanded in terms of amplitudes, which for nonzero mass transform like the wavefunctions for irreducible representations of the proper, orthochronous, inhomogeneous Lorentz group. A simple algorithm was given to obtain the expansion. In the present paper, we extend the results to include zero-mass amplitudes. It is shown that for wavefunctions which are required to transform under the homogeneous Lorentz group such that the matrices which involve the spinor indices are finite dimensional, the zero-mass amplitudes transform under nonunitary representations of the inhomogeneous Lorentz group. However, it is possible to split up each such nonunitary representation into a part which corresponds to a unitary representation for finite spin and into a part which corresponds to an unphysical change of wavefunction. As examples of the technique, we consider wavefunctions which transform as an antisymmetric real tensor (i.e., as an electromagnetic field) as a four-vector with and without the Lorentz condition, and as a Dirac spinor. The results offer interesting contrasts with the reductions of Part I where only nonzero-mass components were considered. It is shown that the expansion of the present paper, when applied to the solution of Maxwell's equations, leads to an expansion in terms of photon wavefunctions and that the unphysical change of wavefunction is zero. For a real vector potential with the Lorentz condition (i.e., the electromagnetic vector potential), the expansion corresponds to the sum of an expansion in terms of photon wavefunctions and a wavefunction which sets the gauge of the vector potential. The nonphysical part of the transformation of the electromagnetic vector potential is merely a gauge change. Finally, solutions of the massless Dirac equation are expanded in terms of wavefunctions for massless particles of spin ½ for which the nonphysical part of the change is zero. In the present paper, we also show how invariant inner products are to be introduced, how negative-energy representations can be replaced by positive-energy representations (''antiparticles''), and show the connection with the usual canonical formalism. Finally, second quantization of the theory is given.
Scattering of Massless Scalar Waves by a Schwarzschild ``Singularity''
Authors: Matzner Richard A.
Published: February 2004

This paper investigates the scattering and absorption of scalar waves satisfying the equation φ;μ;μ=0 in the Schwarzschild metric. This problem has been previously considered by Hildreth. We find, for a Schwarzschild mass m, the following cross sections in the zero-frequency limit for s-waves: σ(absorption) = 0, dσ/dΩ ≃ [c + ⅓(2m) ln (2mω)]2, where c is a constant of order m. These results disagree with the previous calculation. We exhibit a method of solution for the equation. Its limiting (Newtonian) form, with suitable identification of the coefficients, is the problem of Coulomb scattering in non-relativistic quantum mechanics. By demanding coordinate conditions which for large l allow the usual Coulomb results in a partial-wave expansion, we are able to define a partial-wave cross section. The (summed) differential cross section for small frequencies inherits the logarithmic behavior of the s-wave part, which is the only contribution explicitly calculated. (The l ≠ 0 contributions and the behavior of the cross sections for ω ≠ 0 are qualitatively indicated.) Cosmological considerations are given which cut off this divergence.
Further Generalized Bose Condensation, Anisotropic ODLRO and Thin 4He Films
Authors: Carmi Gideon
Published: February 2004

This paper contains a detailed analysis of the Bose condensation of an ideal Bose gas, finite in one dimension and infinite in the other two. Limiting processes, which were treated questionably in previous work, are here re-examined, and some seemingly paradoxical conclusions of the past work are explained. Two new concepts emerge—those of ``further generalized Bose condensation'' (FGBC) and ``anisotropic off-diagonal long-range order'' (AODLRO). The two concepts are shown to be connected to each other, and both are shown to exist at T = 0 for the model discussed.
Padé Approximants and Bounds to Series of Stieltjes
Authors: Common A. K.
Published: February 2004

Series of Stieltjes with nonzero radius of convergence R have been considered in this paper. It is well known that sequences of Padé approximants to these series may be defined which converge in the complex plane cut from −R to − ∞. It is shown that the Padé approximants satisfy inequalities between 0 and −R which are much more general than those already proved on the positive real axis. A new sequence of approximants is defined, which are closely related to the Padé approximants and which have very similar properties. The two sets of approximants may be used to determine the series of Stieltjes within certain limits for points on the real axis between 0 and −R, given only the first few coefficients of the power series expansion. The result is then extended to all points in the interior of a circle with center at the origin and radius R.
Related First Integral Theorem: A Method for Obtaining Conservation Laws of Dynamical Systems with Geodesic Trajectories in Riemannian Spaces Admitting Symmetries
Authors: Katzin Gerald H. , Levine Jack
Published: February 2004

In this paper we develop in detail a unified method, referred to as the Related First Integral Theorem, for obtaining ``derived'' first integrals (i.e., constants of the motion) of mass-pole test particles with geodesic trajectories in a Riemannian spece. By this method, which is based upon a process of Lie differentiation, additional conservation laws in the form of mth order first integrals can be generated from a given mth order first integral (conservation law), provided the space admits symmetries in the form of continuous groups of projective collineations (which include affine collineations and motions as special cases). We give in tensor form a reformulation of the well-known Poisson's theorem on constants of the motion for particles with geodesic trajectories. We then show for this class of trajectories that, as a method for generating mth order first integrals from a given mth order first integral, Poisson's theorem is a special case of the Related First Integral Theorem. It is also shown that dependency relations between generically related first integrals obtained by the Related First Integral Theorem are expressible in terms of the structure constants of the underlying continuous group of symmetries.
Values of the Potential and Its Derivatives at the Origin in Terms of the S-Wave Phase Shift and Bound-State Parameters
Authors: Calogero F. , Degasperis A.
Published: February 2004

The framework of this paper is the quantum-mechanical theory of nonrelativistic scattering of a particle by a spherically symmetrical, local, and energy-independent potential. The principle results are explicit expressions for the values at the origin of the potential and of its derivatives in terms of the S-wave scattering phase shift and of the parameters of the S-wave bound states (if any). Previous work in this direction is reviewed, and different routes to the establishing of these results are discussed. Some remarks concerning the characterization of S-wave physically equivalent potentials (i.e., potentials having the same S-wave phase shift and S-wave binding energies) are presented. The properties of the S-wave phase shift and bound state parameters which are necessary and sufficient to ensure that the corresponding potential be an even function of r are ascertained. The analysis is restricted to potentials represented by holomorphic functions of r.
Unitary Representations of the Generalized Poincaré Groups
Authors: Novozhilov Yuri V. , Terentjev Igor A.
Published: February 2004

The problem of the explicit construction of unitary representations is solved for the generalized inhomogeneous Poincaré groups ISL(n, C) and their subgroups. As a key to the solution, a method is developed to find the generalized Wigner operator, which transforms a given n2 momentum to the standard one. Results are also specified for the U(m, m) subgroup of the group ISL(2m, C).
Note on Statistical Mechanics of Random Systems
Authors: Burke T. , Lebowitz J. L.
Published: February 2004

We discuss some equilibrium properties of random systems, i.e., systems whose Hamiltonian depends on some random variables y with a distribution P(y) which is independent of the dynamic state of the system. For a system of noninteracting particles which interact with randomly distributed scattering centers, the important quantity is the average density of states of a single particle per unit volume, n(E). Feynman's path-integral formulation of quantum statistics is used to derive some properties of the average partition function for one particle 〈Z1〉, which is the Laplace transform of n(E). In particular, it is shown that 〈Z1〉 is an analytic function of the density of scatterers ρ for a wide class of particle-scattering center potentials V(r), including those with hard cores and those with negative parts. The analyticity in ρ of the equilibrium properties of these systems is very remarkable and is in contrast to the conjectured nonanalytic behavior of their transport (i.e., diffusion) coefficients. We find also upper and lower bounds on 〈Z1〉 for a particle acted upon by a random potential V(r) obeying Gaussian statistics with 〈V(r)V(r′)〉∼exp [−α2(r−r′)2]. In the limit of ``white noise,'' 〈V(r)V(r′)〉∼δ(r−r′), 〈Z1〉 is shown to diverge in two and three dimensions but remains finite in one dimension. This agrees with approximate results on the density of states. In appendices we prove the existence, in the thermodynamic limit, of the free-energy density of a system with random scatterers and also of the frequency distribution and, thus, the free-energy density for a random harmonic crystal.
Quantum Corrections to the Second Virial Coefficient at High Temperatures
Authors: Hill Robert Nyden
Published: February 2004

The Laplace transform of exp (−βH) is the Green's operator of the negative-energy Schrödinger equation (H + W)−1. Conditions are stated under which a large |W| asymptotic series for the Green's operator can be inverse-Laplace-transformed term-by-term to obtain a small β expansion for exp (−βH). This approach and the Watson transformation are used to calculate the first few terms of high-temperature asymptotic expansions for the exchange second virial coefficient for hard spheres and for the Lennard-Jones potential. The known results for the direct second virial coefficient for hard spheres are extended. The Wigner-Kirkwood expansion is calculated to order ℏ6 and used to calculate the direct second virial coefficient for the Lennard-Jones potential through order ℏ6.
Green's Functions for the Ising Chain
Authors: Bialynicki-Birula I. , Piasecki J.
Published: February 2004

The Ising chain is represented as a system of fermions interacting through two-particle forces. All thermodynamic Green's functions are calculated exactly in this model. They exhibit many properties expected on the basis of general theory for Green's functions of the interacting particles.
Possible Kinematics
Authors: Bacry Henri , Lévy-Leblond Jean-Marc
Published: February 2004

The kinematical groups are classified; they include, besides space-time translations and spatial rotations, ``inertial transformations'' connecting different inertial frames of reference. When parity and time-reversal are required to be automorphisms of the groups, and when a weak hypothesis on causality is made, the only possible groups are found to consist of the de Sitter groups and their rotation-invariant contractions. The scheme of the contractions connecting these groups enables one to discuss their physical meaning. Beside the de Sitter, Poincaré, and Galilei groups, two types of groups are found to present some interest. The ``static group'' applies to the static models, with infinitely massive particles. The other type, halfway between the de Sitter and the Galilei groups, contains two nonrelativistic cosmological groups describing a nonrelativistic curved space-time.
Inverse Functions of the Products of Two Bessel Functions and Applications to Potential Scattering
Authors: Mavromatis H. A. , Schilcher K.
Published: February 2004

Inverse functions of products of two Bessel functions jl(xy)jm(xy) are determined for the cases m = l, l + 1, and l + 2. Integral representations for these inverse functions in terms of Neumann functions are given, and some of the simplest ones are expressed in terms of trigonometric functions.

We show how one may obtain an integral representation for any well-behaved function in terms of products of two Bessel functions, with the help of these inverse functions and also outline some of their applications to potential scattering. In particular, we demonstrate the usefulness of the inverse functions in determining the potential explicitly from the phase shifts in the Born approximation.