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The scattering cross section (SCS) is a key property in plasmonic studies that carries valuable information on the scattering dynamics. Due to the complexity of fields and the interference from evanescent waves in the near-field region, the SCS is currently calculated in the far-field, which makes the computation costly. In this study we prove analytically that the total SCS is independent of the distance between the closed surface used to calculate the SCS and the scattering structure, hence introducing a numerically inexpensive approach to computing the total SCS, based solely on near-field information. We carry out also two numerical tests of this analytical proof in discretized spaces, verifying its applicability in computations.

A theoretical calculation was performed to evaluate the photo-induced electron transfer (PIET) rate between a gold atom and a gold ion solvated in carbon tetrachloride (CCl4) in the framework of Marcus electron transfer (ET) theory, including both solvent reorganization effects and electronic wavefunction coupling between the ET diabatic states. A novel component of this work involves calculation of the electronic coupling strength using a recently developed constrained real-time time-dependent density-functional-theory (CRT-TDDFT) method. It is found that the PIET rate reaches its maximum value at the electronic resonance wavelength regardless of the inter-particle separation, suggesting a strong correlation between PIET and light absorption. In comparison with thermally activated electron transfer (TAET) at room temperature, light irradiation is demonstrated to be much more efficient than thermal fluctuations in promoting long-range ET, at least for the most common situations, when the light travelling substantially exceeds thermal energy. This work is the first step towards a quantum theory of plasmon enhanced electron transfer, and the theory can also be used to calculate electron transfer rates quite generally for condensed phase problems.

Significant quantum effects in chemistry range from static structure (electronic and geometrical) through dynamical behavior, including optical properties, conductance, relaxation, decoherence, and thermalization. We outline seven situations in which molecular systems exhibit ineluctably quantum behavior. These range from situations in which the community can understand the problem quantitatively and conceptually (for example for dilute sets of spins in NMR) to femtosecond/attosecond situations, which the community understands only primitively. In condensed phase, the dynamics will always evolve in a system/bath environment, and we discuss here how to pose, and to start understanding, problems of that sort.

Using Monte Carlo simulations, we study lateral electronic diffusion in dense monolayers composed of a mixture of redox-active and redox-passive chains tethered to a surface. Two charge transport mechanisms are considered: the physical diffusion of electroactive chains and electron hopping between redox-active sites. Results indicate that by varying the monolayer density, the mole fraction of electroactive chains, and the electron hopping range, the dominant charge transport mechanism can be changed. For high density monolayers in a semi-crystalline phase, electron diffusion proceeds via electron hopping almost exclusively, leading to static percolation behavior. In fluid monolayers, the diffusion of chains may contribute more to the overall electronic diffusion, reducing the observed static percolation effects.

Light transmission and electric field enhancement are calculated for a cylindrical aperture in a silver slab resting on a glass substrate. We find that these properties are influenced significantly by the presence of the substrate. The results suggest that variations in the local dielectric alter the properties of localized surface plasmons that drive the field enhancement and transmission.

Photodissociation of I 2 in the I 2 Ar 17 cluster is studied by quantum wavepacket simulations, using time-dependent mean-field potentials. It is found that: (a) Initial energy transfer from the I 2 is mostly to three cluster modes, which undergo multiquantum excitation. Several other modes undergo single-quantum excitation. (b) Coherent phase transfer from the I 2 to specific cluster modes is found. (c) Energy transfer from initially-excited modes to the other modes becomes large after 0.6 ps. Phase space interpretation is provided by computed Wigner distributions in time.

We have derived an approximate analytic expression for the spectral density of a simple model of a semiconductor/molecule junction. The semiconductor is considered as a tight-binding one-dimensional chain with periodic boundary conditions, and either bond or site-energy alternation, to mimic a two-band system. Using the simplest representation for an atomic or molecular site we obtain a spectral density whose main physical and mathematical features are independent of the alternation pattern. Our model can be applied to the description of transport properties in many complex junctions. Here, we have explored its simplest consequences in the calculation of the transmission coefficient for a junction consisting of a semiconductor electrode, a molecular site and a metal electrode.

We suggest here a family of non-linear optical chromophores that have weak response in the ground state and a significantly enhanced response in the triplet state – hence a non-linear optical ‘switch’. Several promising molecules are proposed and their response mechanism, in which computation shows a significant enhancement of the first hyperpolarizability upon photoexcitation from the singlet to metastable triplet state, are investigated.

The relation between intra-molecular electron transfer in the donor-bridge-acceptor system and zero-bias conductance of the same bridge in the metal–molecule–metal junction is analyzed for the sequential hopping regime of both processes. The electron transfer rate and molecular conductance are expressed in terms of rates characterizing each individual step of electron motion. Based on the results obtained, we derive the analytical expression that relates these two quantities in the general case of the energy landscape governing hopping transport.

We present the multipole Taylor series expansion of the Debye–Huckel potential exp(− R / κ )/ R for screened electrostatic interactions, where R is the separation distance and κ is the Debye length. Based on that expansion we derive the expressions for the electrostatic field and interaction energy in the cases of charge–dipole, dipole–dipole, and quadrupole–dipole interactions. The results are compared with a recent expansion of the same potential based on modified spherical Bessel functions [A. Boschitsch, M.O. Fenley, W. Olson, J. Comput. Phys. 151 (1999) 212]. Some examples illustrating the limits of validity of the derived formulae are presented, and their possible applications are discussed.

Simple electronic structure models are used to address two significant challenges in organic materials chemistry, the design of chromophores for strong electro-optic response (and low-energy optical absorption), and the prediction of relative mobilities and charge injection barriers for conductive oligomers. For electro-optic response, we examine two chromophore classes where twisting around an inter-ring bond can tune the electronic structure from aromatic (zwitterionic) to quinoid (neutral). The calculated nonlinear response develops a very strong maximum ( β μ ∼ 1500 ×10 −30 esu) at twist angles near 80°. For the transport behavior, structure/function correlations are presented for three series of oligomers, based on calculations of bandwidths (as functions of geometry) and of reorganization energies. Transport type appears to be fixed less by these mobility factors than by the injection barriers. The simplest estimates for these Schottky-type barriers, using frontier orbital energies from density functional calculations, predict carrier n-type or p-type behavior remarkably well.

We report here the first phase in the rational design of a versatile hydrogen-bonded supramolecular `zipper', by creating a molecular `tool box'. These are novel structures that are predicted to undergo self-assembled and to form stable `zippers', which should be amendable to molecular manipulations that change the physical properties of the supramolecule, while preserving the three-dimensional structure. We emphasize design rationale, including examples, and also demonstrate the importance of using highly accurate computational methods in molecular design.

The I–V curves are computed for 2,7-dithiolpyrene and 4,4′-dithiol-diphenylacetylene between two Au(1 1 1) surfaces. For a given bias, up to about 2.5 eV, the current for 2,7-dithiolpyrene is about half that for 4,4′-dithiol-diphenylacetylene. However, the fused benzene rings in 2,7-dithiolpyrene eliminate the loss of current associated with rotation about the central C2 that can occur for 4,4′-dithiol-diphenylacetylene.

Twisted, merocyanine-type molecules are investigated theoretically as chromophores, whose optical and electro-optic responses can be controlled via steric repulsion-mediated tuning of the central dihedral angle. Employing multi-reference determinant computational methods results in significant modifications to the quantitative aspects of the response properties, compared to values computed using a single determinant ground state, and leads to computed hyperpolarizabilities even larger than previously estimated. Using either computational approach demonstrates that fine control of the sharp variations in response properties can be achieved by using substituent-induced steric repulsions to modify the internal dihedral twist angles.

In a coarsened description of glassformers, the fluctuating variable is the local order. The configuration space of a glassformer consists of many basins with basin boundaries determined by heights of the potential energy landscape. We suggest that structural changes in the system may be described in terms of local rearrangements as elementary inter-basin steps. A general theorem is found relating the fluctuations of the local structure to thermodynamic properties measured at different time scales.

We study dielectric properties of metallic systems using a modified Pariser-Parr-Pople model in the single determinant approximation. Our model does not invoke extra screening; it describes long-range coulomb interaction exactly and approximates and neglects only the short-range exchange and correlation effects. We show that in metallic systems this long-range coulomb interaction leads to spatial localization of electronic orbitals over several atoms, different from orbital localization on single atoms in Mott insulators. We speculate that such localization is also important for the description of metallic transport properties based on Hartree–Fock or Kohn–Sham density functional theory formalisms.

Although conductance measurements of single molecule and few molecules junctions are currently being reported, there is a striking rarity of molecular rectification in these reports. Molecular rectification can be defined as the absence of inversion symmetry, IðV Þ¼ � Ið� V Þ, where I and V are the measured current and applied voltage. In molecular junctions of the form metal/molecule/metal, there is generally an absence of structural mirror symmetry. One might then expect rectification arising from this asymmetrical structure. We suggest here that molecular rectification in tunneling junctions is generally difficult to achieve, essentially because deformation of the structure in the presence of finite voltage will result in effectively symmetric voltage profiles for forward and reverse biases. 2002 Elsevier Science B.V. All rights reserved.

Electron transfer (ET) reactions in donor–bridge–acceptor (DBA) molecules that occur by means of superexchange interactions between the donor (D) and the bridge (B) molecules depend on the vertical energy gap separating D and B. This dependence modulates the electronic coupling matrix element for ET, and hence the ET rate. However, when the energy gap between D and B is small, the assumptions intrinsic to the simplest superexchange model break down and charge injection from D to B may occur. To investigate this range of possibilities, we synthesized a family of DBA molecules based on a 2,5-bis(2 ′ -ethylhexyloxy)-1,4-distyrylbenzene (OPV3) bridge. Three electron donors, zinc 5,10,15,20-tetraphenylporphyrin (ZnTPP), perylene (PER) and tetracene (TET) as well as two electron acceptors naphthalene-1,8:4,5-bis(dicarboximide) (NI) and pyromellitimide (PI) were attached to the OPV3 bridge. The observed ET dynamics of these molecules are sensitive not only to the donor–bridge energy gap, but also to the excited state torsional dynamics between the donor and bridge.

Monte Carlo calculations were carried out to simulate ion diffusion through polymer matrices. A dynamic bond percolation (DBP) model was employed that includes local harmonic motion of covalently bound anions in polyelectrolyte systems. The temperature dependence of cation diffusion was investigated in polyelectrolytes and polymer–salt complexes for 0–100 °C. Systems in which the rate of polymer reorganization is independent of temperature display Arrhenius behavior both above and below the Tg of 35 °C. Systems in which the temperature is coupled to the rate of polymer reorganization display VTF behavior above the Tg and near Arrhenius behavior below the Tg. In all cases, the temperature is coupled to the rate of successful ion jumps. Temperature and Tg seem to have no effect on the ion density at which the cation conductivity reaches a maximum.

A recently presented dielectric continuum model is extended to a metal coated with two dielectric layers. The potential energies, binding energies and wave functions of the image potential states are presented as a function of the electron affinities and dielectric constants of the dielectric media. The double dielectric continuum model (DDCM) is compared with the single dielectric continuum model (SDCM). The heterogeneous reaction field solvation model enables the computation of the dielectric constant of a molecular layer adsorbed on the surface of a perfect conductor. The dielectric constant is presented as a function of the orientation of the molecule relative to the surface of the perfect conductor. The computed dielectric constants are used for computing the binding energies and wave functions of the lowest lying electron states of a Cu(1 1 1)-surface covered with a monolayer or bilayer of benzene. The estimated binding energies are compared with the ones measured experimentally by Velic et al. [J. Chem. Phys. 109 (1998) 9155].

Molecular electronics and optoelectronics depend for their existence on the molecular organization of space. The fundamental mechanisms underlying the rich phenomena that have been discovered in these areas arise from mixing of electronic energies in the molecule with external, macroscopic structures. Mechanisms of charge injection and transport, and their manifestations in the physical properties of molecular electronic junctions, are discussed. Major questions that remain unresolved are placed in the contexts of fundamental understanding and device considerations. In the natural world, molecules are used for many purposes. Using molecule-based materials for electronics, sensing, and optoelectronics is a new endeavor, called molecular electronics, and the subject both of riveting new research and substantial popular press interest.

Using stacks of Watson–Crick base pairs as an important example of multichromophoric molecular assemblies, we studied charge migration in DNA with special emphasis on the mechanism of hole hopping between neighboring guanines (G) connected by the adenine–thymine (AT) bridge. The tight-binding model proposed for this elementary step shows that for short AT bridges, hole transfer between two G bases proceeds via quantum mechanical tunneling. By contrast, hopping over long bridges requires thermal activation. The condition for crossover between tunneling and thermal activation near room temperature is specified and applies to the analysis of experimental data. We show that thermal activation dominates, if the bridge between two G bases contains more than three AT pairs. Our theoretical findings predict that the replacement of AT base pairs by GC pairs increases the efficiency of hole transport only in the case of short base pair sequences. For long sequences, however, the opposite effect is expected.

The quantum dynamical semigroup formalism provides an appealing general framework for discussing factors that affect pure vibrational dephasing rates in chemical systems. Within this framework, we formulate a Poisson model of pure vibrational dephasing which is more generally applicable than the commonly employed stochastic Gaussian dephasing model. In the limit of small and frequent phase changes, the Poisson model reduces to the stochastic Gaussian form. We find that for certain vibrational states of the lithium dimer in argon, the stochastic Gaussian model is valid, while for other states large and abrupt phase changes clearly require application of the Poisson model. In the former case, dephasing rates increase with the difference in quantum number between constituent vibrational states, while in the latter case, the dependence on quantum number difference or energy gap can become negligible. Recent experimental advances described by Amitay and Leone are expected to permit experimental tests of our theoretical predictions.

An analytical expression is obtained for the I – V curves for a tight-binding model of a molecule–metal junction for off-resonance injection. The derivation takes into account a self-consistent determination of the voltage that leads to a spatial pattern where the voltage drop occurs at the molecule–wire interface. The relevance of this model for electron transfer reactions and molecular conductance is assessed. It leads to a striking power law dependence of the current on the voltage, while preserving the exponential length dependence of either the conductance or the reaction rate.

A series of polymer salt complexes based on poly(ethylene malonate) and lithium triflate were prepared with polymer repeat unit to cation ratios of 8, 4, 2, 1. These were characterized and then mixed with lithium triflate. The CO stretching peaks in the IR spectra of these polymers became broad when salt was introduced, indicating complex formation between the polymer and the lithium cation. Pure poly(ethylene malonate) has a glass transition at 258 K and the glass transition temperature increases with increasing salt concentration. The maximum room temperature ionic conductivity for this polymer/salt complex is 1.6×10−6 S/cm for a polymer repeat unit to cation ratio of 8, and the temperature dependence of the conductivity follows the Vogel–Tammann–Fulcher (VTF) equation.

Physical mechanisms that might assure the functioning of DNA as a molecular wire are considered on the basis of recent progress in understanding long-range charge transfer in this biologically important molecule. Our analysis shows that DNA behaves as an insulator at low bias, while beyond the threshold the current sharply increases. Such behaviour concurs with recent experimental observations and is explained by the decrease of the energy gap between the HOMO of guanine bases and the Fermi level of the contact with the voltage applied across the individual DNA molecule. We propose a model for the hole injection in DNA, which is based on the dynamic control of this process by internal motions of base pairs in the stack. The temperature dependence of the voltage gap obtained within this model is found to be in reasonable agreement with the available experimental data. For systems, where charge transfer is controlled by changes in the relative orientation of the donor and acceptor and where the equilibrium states are optimally overlapped, the model predicts the decrease of the tunneling transfer rate with temperature. We also demonstrate that depending on the structure of the stack, hole transport along DNA wires above the voltage threshold can proceed via two different mechanisms. In the case of duplex DNA oligomers with stacked adenine–thymine and guanine–cytosine pairs migration of injected holes can be viewed as a series of short-range hops between energetically appropriate guanine bases. By contrast, in double-stranded poly(guanine)–poly(cytosine) the band-like motion of holes through bases dominates.

In this Letter, we report optimized structures and lithium affinities of a series of anionic zeolitic fragments [H 3 Al(OCH 3 ) x (OSiH 3 ) 1– x − 2T, H 2 Al(OCH 3 ) x (OSiH 3 ) 2– x − 3T, Al(OCH 3 ) x (OSiH 3 ) 4– x − 5T] that mimic the charge sites in polyelectrolytes. Ab initio molecular orbital methods at different levels of theory are used. The lithium affinities are much larger than the corresponding sodium affinities, indicating stronger interactions between lithium cations and these zeolitic fragments. The substitution of silicon by carbon increases the lithium affinity and the effect is generally larger than in the sodium systems.

A Huckel-type effective Hamiltonian is used to examine the conditions for site-selected reactivity. The example is the dissociation of a positive ion, as in mass spectrometry. Coupling to the dissociative channels is included by a rate operator. We examine the time evolution of the charge and bond order matrices and of the yield of fragments following a localized initial ionization. Dissociation is found to follow the (positive) charge. Variations in the local properties can markedly change the dissociation pattern. A more statistical limit is reached when the migration of charge is unimpeded.

A coarsened model for a binary system with limited miscibility of components is proposed; the system is described in terms of structural states in small parts of the material. The material is assumed to have two alternative types of crystalline local arrangements associated with two components of the alloy. Fluctuating characteristics of a cluster are the type and the space orientation of its crystalline arrangement. There are two different phase transitions in the model system, an orientation order-disorder transition representing melting, and a phase transition between phases differing in concentration of components. Depending on the parameters characterizing the interaction in the system, this last transition may take place both in the crystalline and in the amorphous (molten) phase. A special approximation is used to study the thermodynamics of the system. The calculated phase diagram describes, at least qualitatively, the most important features of a binary system.

In this article we discuss the problem of well-defined crystalline patterns of local atomic arrangements in equilibrium liquids, and their statistical mechanics modelling. We present arguments in favor of the existence of local crystalline structures in liquids (local crystal order hypothesis) and discuss a generalized energy landscape picture in the theory of the liquid state. This picture allows a quantification of the hypothesis of local order and offers basic concepts for the statistical mechanics modelling of the melting phase transition. We review recent results of probabilistic-based searches for local structures in various two- and three-dimensional computer-simulated liquids. Next, some statistical-mechanics models of melting and amorphization in terms of structural states of small clusters are proposed. The models, which have only two characteristic energies, that of the orientationally disordered locally crystalline state, and that of completely amorphous state, are studied in a mean-probability approximation. If the amorphization energy is high, the material retains local crystallinity even in the melt; at higher temperatures a crossover to the locally amorphous state occurs. A material that has a low energy non-crystalline local packing exhibits an amorphization melting; the phase transition is from orientationally ordered crystal state to a locally amorphous melt.

New polymer electrolytes were synthesized and characterized based on a new polymer host. The motivation was to produce a host polymer with a high dielectric constant which should reduce ion clustering with an attendant increased conductivity. The new polymer host, poly(diethylene glycol carbonate) and its sodium triflate complexes were characterized by thermal analysis and AC impedance measurements. The polycarbonate backbone appears less flexible than the polyether hosts as evidenced by the higher glass transition temperatures. The conductivity for the sodium triflate complexes was measured as ~ 10−5 S cm−1 at 55 °C and the dielectric constant of the host polymer was found to be 3.6 at 3 GHz. The low conductivity is attributed to rigidity of the polycarbonate.

We analyse the concurrency and performance of the various types of force calculations involved in the molecular dynamics simulation of large protein or polyelectrolyte molecules. Although this analysis can in principle be used to write a meta-program to optimize load-balancing of this application on an MPP system, we argue that it is an enormous undertaking not appropriate for the computational scientist. Instead we argue that it is better to exploit research in parallel execution environments which provide automatic load-balancing for concurrent Object-Oriented applications. We also argue that use of Object-Oriented technology in the design of simulation software encapsulates the natural concurrency of the system. We illustrate this point with a discussion of the constraint force calculation for a polymeric molecule.

A nitrobenzene (NB) decorated cadmium sulfide cluster, [Cd4(SNB)10][N(CH3)4]2, has been prepared and examined spectroscopically. The assembly exhibits an intense cluster-to-attached-acceptor charge-transfer band at 376 nm. Observation of back electron transfer (nitrobenzene to cluster) via time resolved luminescence yields a rate constant of ≥ 5 × 109 s−1. Raman studies show that seven vibrational modes are coupled to the electron transfer reaction and that those exhibiting the greatest initial-state/final-state displacements are the CdS and NO stretches. Despite the activity of νCd-S, however, the electron donor is more appropriately characterized as an individual sulfur atom, rather than a delocalized assembly.

We discuss situations occurring in intramolecular electron transfer in glassy solvents and in proteins which themselves undergo glassing transitions. In these circumstances slow solvent relaxation causes the reaction pathway to vary substantially from the equilibrium reaction path, resulting in increased effective barriers and reduced effective outer-sphere reorganization energies compared to the transition-state (equilibrium) result. This effect is modelled simply by introducing a temperature dependent reorganization energy. Through inclusion of these non-equilibrium effects, sharp falloffs of electron transfer rate with decreasing temperature can be modelled with reasonable values of the equilibrium reorganization energy, rather than the inappropriately large values needed otherwise.

Current–voltage characteristics of gold-benzene-1,4-dithiol-gold junctions are calculated using a combined density functional theory/non-equilibrium Green's functions approach with local atomic basis sets. Improving the basis set with the addition of polarization or diffuse functions has some effect on the computed I – V curves, but even the small valence double zeta sets yield reasonable results. The results obtained using the hybrid B3LYP functional give slightly smaller conductance than those obtained using the pure BPW91 approach. Substituting Cl for H on the bridging molecule has only a small effect on the I – V curves.

Simulations implementing both Monte Carlo (MC) and molecular dynamics (MD) techniques were used to explore various aspects of polymer electrolytes. Evidence is presented to support the conclusion that collective behavior of ions determines much of the behavior of these complex materials. Simple theories attributing ion transport to either single ions or clusters of three ions are inadequate to explain ion transport behavior; in particular, the Nernst-Einstein relation commonly used to discuss polymer electrolytes is almost certainly quantitatively inappropriate for these materials.

Model systems of sodium iodide dissolved in dimethyl ether or 1,2-dimethoxyethane (glyme) were studied in order to investigate the structural and dynamic properties of ionic solutions in small and polymeric ethers. Full molecular dynamics simulations were performed at a range of different salt concentrations. An algorithm was designed which assigns ions to clusters and then calculates all the terms which contribute to ionic conductivity. In dilute solutions, free ions are the most common ionic species, followed by ion pairs. As the concentration increases, pairs become the most common species, with significant concentrations of clusters with 3 through 6 ions. Changing the solvent from dimethyl ether to glyme significantly decreases the ion clustering due to the chelate effect in which the two oxygens on a solvent stabilize an associated cation. The conductivity in stable systems is shown to be primarily the result of the movement of free ions and the relative movement of ions within neutral pairs. The Nernst-Einstein relation, commonly used in the discussion of polymer electrolytes, is shown to be inadequate to quantitatively describe conductivity in the model systems.

Profound changes in the metal-centered electroactivity of thin-film redox polymer/electrolyte systems accompany the replacement of a conventional electrolyte solution (aqueous tetraethylammonium perchlorate) by any of several aq. CH3(CH2)SO3-Na(+) solutions. For example for a poly-Fe(4-methyl-4'-vinyl-2, 2'-bipyridine)3m+ film in contact with an aq. sodium decanesulfonate solution: (a) the overall redox capacity decreases by roughly half an order of magnitude, (b) the rate of hopping-based electron transport during charging decreases by 20-fold, and (c) the thermodynamic potential for metallopolymer oxidation moves to a significantly less positive value, in comparison to films equilibrated with conventional solutions. Further experiments show that the modulation behavior is associated with the uptake and release of charge-compensating anions during film oxidation and reduction (i.e. cations are excluded), that the degree of modulation increases with increasing counter anion size, and that the modulation phenomenon is chemically reversible. These unusual effects are tentatively attributed to polymer-based steric constraints on large alkanesulfonate ion incorporation, together with hydrophobic partitioning effects. These factors apparently conspire to couple film-based electron motion strongly to counter- anion motion. Finally, spectroelectrochemical measurements show that CH3(CH2) 9SO3-containing-films are reversibly confined to a predominantly mixed-valent form (Fe(II)+Fe(III)), even at electrochemical potentials for removed from the formal potential for redox processes in the film.

Random lasing attracts much attention because it helps to understand coherent phenomena in disordered media and can be used in optoelectronics due to easy preparation (no need in mirrors) and small size of random lasers down to few microns. Recently the remarkable progress in studying the material, geometry and external pumping dependences of laser properties and efficiency has been reached. Lasing emerges from the special random cavities of high quality formed within the active medium. They can be described as the decaying eigenoptical modes within the medium and the optical mode having the minimum decay rate is responsible for lasing. Numerical and analytical studies of the properties of these modes permit to interpret existing experiments and suggest the ways to optimize the performance of lasers.

The golden-rule expression for the non-adiabatic electron-transfer rate constant in donor/acceptor system is analyzed using a Fourier (time-dependent) representation. The rate constant is written in terms on an evolving overlap of wavepackets on initial and final state potential-energy surfaces. By the following the explicit time-dependence of these functions, we can obtained both standard results of electron-transfer theory for the specific case of a standard polaron-type model (including inverted-region behavior, temperature dependence, nuclear tunneling effects, energy sharing) and some important generalizations, including situations of breakdown of the Condon approximation, analysis of the effects of the frequency changes, and simplifications of the relevant vibrational modes due to solvent, to intra-molecular vibrations, or to both. The correlation-function method is briefly described, and results of a number of calculations are discussed. Analysis includes the effect of inhomogeneous broadening and energy flow into solvent and vibrational degrees of freedom. Analysis of two particular cases, subjects of recent elegant experimental investigation, are included to show the applicability of the technique.

We discuss the possibility of using the energy of the transmitted electron (ϵ) as a control parameter in electron transfer (ET) reactions. The change in response of the system is entirely contained, within the simplest model, in the effective electronic coupling, which exhibit sharp changes in the resonance region and near its minima as a function of ϵ. The positions of the minima are strongly influenced by the molecular geometry. To calculate the effective coupling, we use a Green's function approach. The electronic structure is calculated within an extended Huckel model. We show the interference and resonance behavior appears for a very simple a four-site model with multisite interactions. The interference effects disappear in a tight binding model of the same system. Application to a molecular system dramatically shows these effects.

Diffusion in concentrated ionic solutions involves ionic motion subject both to interionic Coulomb forces and to the fluctuating potentials arising from solvent motion. To study how these reflect themselves in the ion transport, we examine a problem in which Coulomb particles hop on a lattice that is percolative (some jumps are forbidden) and renewing (the forbidden jumps evolve in time). Diffusivity and tracer correlation are both effected by both renewal and Coulomb interaction. Coulomb effects can destroy the validity of the dynamic percolation result that the diffusivity is proportional to the renewal rate; non-exponential decay of the energy fluctuation correlation function is observed.

An anomalous power law behavior of spectral diffusion broadening of persistent holes is found in large biological molecules dissolved in a glassy host at very low temperature. We argue that this is caused by the internal degrees of freedom of the biomolecule itself rather than by excitations of the glassy host. To explain the observed universal time dependence of the hole width w ∼ t 1/4 , we propose a stochastic model of protein dynamics close to the equilibrium, which describes this process in terms of the quasi-one-dimensional diffusion of proteins in conformation space. Assuming that each step of diffusive motion changes the electronic excitation energy randomly, we derive the observed time behavior of the spectral hole. The physical mechanisms involved are discussed.

Structural, thermodynamic and transport properties have been calculated in concentrated non-aqueous NaI solutions using molecular dynamics simulations. Although the solvent has been represented by a simplistic Stockmayer fluid (spherical particles with point dipoles), the general trends observed are still a useful indication of the behavior of real non-aqueous electrolyte systems. Results indicate that in low dielectric media, significant ion pairing and clustering occurs. Contact ion pairs become more prominent at higher temperatures, independent of the dielectric strength of the solvent. Thermodynamic analysis shows that this temperature behavior is predominantly entropically driven. Calculation of ionic diffusivities and conductivities in the NaI/ether system confirms the clustered nature of the salt, with the conductivities significantly lower than those predicted from the Nernst-Einstein relation. In systems where the solvent-ion interactions increase relative to ion-ion interactions (lower charge or higher solvent dipole moment), less clustering is observed and the transport properties indicate independent motion of the ions, with higher calculated conductivities. The solvent in this system is the most mobile species, in comparison with the polymer electrolytes where the solvent is practically immobile.

Ionic motion in polymeric ionic conductors has been recently described in the framework of dynamic percolation theory (DPT) or, more generally, dynamic disorder hopping (DDH). In these models the polymer network above the glass transition is modelled as a random bond network in which the random bond distribution evolves in time with rate characteristic to the polymer motion. The present paper deals with the mechanical properties of such networks. We present a simple analysis of the viscosity of such dynamically disordered networks, thus relating a characteristic network relaxation time to the local (microscopic) viscosity of the polymer. If the same time is assumed to govern ionic transport, we obtain a relation between the ionic diffusion rate and the polymer viscosity. Estimates of the ionic diffusion based on this model are consistent with experimental observations.

The conductivity in a phase-separated conductor-insulator composite fiber is found to be quite different from that of a percolating system. There is evidence that the placement of the conducting domains is in an ordered, rather than in a random, manner within the insulating matrix, with the conductivity being limited by tunneling from one conducting domain to another. The conductivity is found to scale as exp(αϕ 1 3 ) over a wide range of conductor volume fractions ϕ.

The major obstacle to the description of systems containing a large number of degrees of freedom is the exponential increase of computational time and effort with dimensionality. A strategy is presented to overcome this obstacle as well as the shortcoming of the omission of correlations, while still maintaining the simplicity and strengths of a mean-field description, based upon identifying the crucial dynamical correlations and incorporating them with multiconfigurations. The collinear reactive scattering of H + H 2 illustrates the techniques involved and their adaptability, flexibility, and breadth of applicability. MCTDSCF simulations, constructed from time-dependent variational principles, are compared with the numerically exact solution of the Schrodinger equation; agreement is found.

The polarized Raman scattering from small single crystals of Cu2HgI4 provided assignments for the more prominent Raman features to specific irreducible representations. The E symmetry assignment, mass dependence, and pressure dependence of the 36 cm−1 band in Cu2HgI4 and 24 cm−1 band in Ag2HgI4 indicate that these features approximate the attempt frequency for ion hopping. The unusually high pre-exponential factor in the Arrhenius expression for ion hopping is discussed in light of the observed attempt frequency; we conclude that despite the high activation energy the conduction mechanism is similar to other heavy-metal solid electrolytes.