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[en] The efficiency of materials developed for solar energy and technological applications depends on the interplay between molecular architecture and light-induced electronic energy redistribution. The spatial localization of electronic excitations is very sensitive to molecular distortions. Vibrational nuclear motions can couple to electronic dynamics driving changes in localization. The electronic energy transfer among multiple chromophores arises from several distinct mechanisms that can give rise to experimentally measured signals. Atomistic simulations of coupled electron-vibrational dynamics can help uncover the nuclear motions directing energy flow. Through careful analysis of excited state wave function evolution and a useful fragmenting of multichromophore systems, through-bond transport and exciton hopping (through-space) mechanisms can be distinguished. Such insights are crucial in the interpretation of fluorescence anisotropy measurements and can aid materials design. Finally, this Perspective highlights the interconnected vibrational and electronic motions at the foundation of nonadiabatic dynamics where nuclear motions, including torsional rotations and bond vibrations, drive electronic transitions.
[en] We present the analytical results at the mean-field level for the asymmetrical fermion system with attractive contact interaction at zero temperature. The results can be expressed in terms of linear combinations of the elliptic integrals of the first and second kinds. In the limit of small gap parameter, we discuss how the asymmetry in fermion species affects the phases of the ground state of the system. In the limit of large gap parameter, we show that two candidate phases are competing for the system's ground state. The Sarma phase containing a pure Fermi fluid and a mixed condensate is favored at a large degree of asymmetry. The separated phase consisting of a pure Fermi fluid and a boson condensate supports the system at a small degree of asymmetry. The two phases are degenerate in the limit of infinite pairing gap
[en] We compute binding energies and root-mean-square radii for weakly bound systems of N=4 and 5 identical bosons. Ground and first excited states of an N-body system appear below the threshold for binding the system with N-1 particles. Their root-mean-square radii approach constants in the limit of weak binding. Their probability distributions are on average located in nonclassical regions of space which result in universal structures. Radii decrease with increasing particle number. The ground states for more than five particles are probably nonuniversal, whereas excited states may be universal.
[en] We discuss the discrepancy between the Cung et al. [Phys. Lett. B 68, 474 (1977)] calculation of the three-photon-annihilation contribution to the positronium ground-state energy, performed using the binding energy to regulate the infrared divergences, and the recent calculation of Adkins, Bui, and Zhu [Phys. Rev. A 37, 4071 (1988)], which used a photon mass to regulate these divergences. By using a simpler version of the binding-energy approach advocated by these authors, we confirm the value of the discrepancy they obtained. Furthermore, it is shown that the additional term needed in the binding-energy approach to produce agreement between the two methods is precisely the one required to make the binding-energy regularized amplitudes gauge invariant to all orders in the binding
[en] A perturbative expansion of the electron's Dirac Coulomb propagator around a nonrelativistic form is used to evaluate the one-loop p nonrecoil corrections to ground-state hyperfine splitting in p hydrogenic atoms. A contribution previously estimated as (α/π)(Zα)2 x (18.36 +- 5)E/sub F/ is found to be (α/π) (Zα)2 (15.10 +- 0.29)E/sub F/. Theory and experiment are compared for muonium hyperfine splitting and consequences for the fine-structure constant are discussed
[en] The geometries and relative energies of the nine lowest states of the ozone molecule have been determined in C/sub 2v/ symmetry from ab initio configuration interaction calculations in a [3s2p1d] contracted Gaussian basis. Calculations were carried out over a two-dimensional grid of points in C/sub 2v/ symmetry to locate the optimum geometrical parameters R and theta for each state. For the ground 1A1 state the calculated properties (with experimental values in parentheses) are as follows: R/sub e/=1.299 A (1.271 A), theta/sub e/=116.00 (116.80), ω1=1235 cm-1 (1110 cm-1) and ω2=707 cm-1 (705 cm-1). Of the excited states only the lowest 3B2 state is found to have an adiabatic excitation energy (0.92 eV) less than the dissociation energy (D/sub e/=1.13 eV) and hence to be a likely bound species. The 1B2 state responsible for the strong absorption in the Hartley band (4.7--5.8 eV) is stabilized by asymmetric distortions away from its equilibrium C2/sub v/ geometry (R/sub e/=1.405 A, theta/sub e/=1080); this finding suggests unequal bond lengths for this state or else purely dissociative behavior. The ring (21A1) state (R/sub e/=1.449 A, theta/sub e/=600) is found to lie 1.20 eV above the ground state, while the remaining five states have adiabatic excitation energies ranging from 1.4 to 3.6 eV. The implications for photodissociation of O3 are discussed
[en] Many important classes of surface reactions exhibit both high heats of reaction and large, positive activation energies. In addition, many surface reactions often occur in thermally isolated environments. As a result, significant autothermic effects are possible. In part I of this article, a generalized model of these effects is presented which describes the enhancement in reaction rate as a function of activation energy, bulk temperature, and a parameter termed the characteristic temperature. Reactant concentration and reaction order effects are also considered. Part II of this work presents the application of this model to numerous experimental plasma etching data
[en] A new method for choosing a reference pair potential for atomic fluids is presented. This method and the optimized cluster theory are used to calculate pair distribution functions for a number of classical fluids. The results indicate that pair distribution functions obtained by this method are very accurate for fluids which have a repulsive pair potential
[en] A new model for the ground-state potential energy curves of heteronuclear diatomic molecules is presented. In this model, applicable equally to covalent and ionic bonds, the total potential energy is decomposed into a covalent and an ionic component whose respective contributions are determined by a quantity f, called bond polarity, which is an accurate measure of the ionic character of a bond. The ionic part of the energy is modeled by the Rittner potential, derived using the implicit perturbation theory formalism, while the covalent part is represented by an empirical potential energy function whose parameters are related to atomic constants obtained from the equilibrium spectroscopic properties of the homonuclear diatomic molecules corresponding to the atoms forming the heteronuclear molecule. The new model is applied in detail to the alkali halides. Employing the Hulburt-Hirschfelder potential energy function to represent the covalent component of the energy. Significant improvement in the predicted values of the spectroscopic constants of these molecules is achieved over the earlier models which all consider the alkali halides 100% ionic molecules
[en] We extend to finite temperature a Green's-function method that was previously proposed to evaluate ground-state properties of mesoscopic clouds of noninteracting fermions moving under harmonic confinement in one dimension. By calculations of the particle and kinetic-energy density profiles, we illustrate the role of thermal excitations in smoothing out the quantum shell structure of the cloud and in spreading the particle spill out from quantum tunnel at the edges. We also discuss the approach of the exact density profiles to the predictions of a semiclassical model often used in the theory of confined atomic gases at finite temperature