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The ground-state energies of an excess electron E0 as a function of solvent density are computed using model electron–atom pseudopotentials in fluid helium, argon, and xenon. E0 is a lower bound to the experimentally measurable threshold to photoconductivity, V0. The nonuniqueness of the pseudopotential description of electron–molecule interactions is demonstrated. We find that when many-body polarization effects are included, our calculated E0 results are in close agreement with experimental V0 values indicating that the conduction-band energy lies close to the ground-state energy across a broad range of densities in these polarizable fluids. If the many-body nature of the polarization interaction is ignored the ground-state energies deviate significantly from the V0 results highlighting the importance of accurate treatment of many-body polarization interactions. It is shown that a mean-field theory of polarization gives substantial agreement with full many-body calculations. This allows us to introduce a mean-field, density-dependent pair potential which greatly simplifies such many-body calculations. In the more polarizable systems, it is found that the spatial extent of the ground-state wave function as a function of solvent density is correlated with the density dependence of both V0 and the electron mobility, and it becomes uniformly spread throughout our simulation cell as the electron mobility goes through its maximum value at intermediate solvent densities. [ABSTRACT FROM AUTHOR]

The structure of an excess electron in water at room temperature is investigated using the Feynman path integral technique. The interaction potential between the electron and water is modeled by an effective potential, made up of three terms: a static potential, a repulsive potential, and a polarization potential. The polarization part is treated in two different ways: approximated as pairwise additive, and exactly with the many body polarization effects treated self-consistently. It is shown that the excess electron forms a cavity with the radius of the electron being 2.24 Å for pairwise additive polarization and 2.11 Å for the self-consistent treatment of the polarization. There is no sharp geometrical coordination number of water molecules around the electron. The water molecules within a distance of about 3.5 Å from the center of the electronic change distribution point their OH bonds towards the electron, and form only three hydrogen bonds. It is also found that the pair correlation function of the solvent molecules close to the electron are considerably different from the corresponding quantities calculated in the bulk. The electron, therefore, is shown to modify the local density to a large extent. There are important structural differences between the many body polarization model and the two body polarization model. It is concluded that for a quantitative description of the structure of the hydrated electron, the self-consistent treatment of the long range (many body) polarization effects are important. [ABSTRACT FROM AUTHOR]

Simulation of e-–(H20)n for n=1,2,3 done at 5 K, using path integral Monte Carlo methods shows that a water dimer as well as a water trimer in the linear configuration can bind an electron in a diffuse surface state. The binding energy of the electron dimer and the electron trimer is estimated to be between 3–6 and 4–9 meV, respectively. The results indicate that the electron does not alter the structure of the water dimer but does induce observable changes in the water trimer. It is also shown that an electron does not bind to a monomer. These results are discussed in connection with recent molecular beam experiments. [ABSTRACT FROM AUTHOR]

An expression for the microcanonical rate constant that can be conveniently evaluated by path integral techniques is proposed. The efficacy of the method is illustrated by obtaining accurate transmission probabilities as a function of energy for a particle tunneling through an Eckart barrier. The application of the method to systems involving many degrees of freedom is discussed. [ABSTRACT FROM AUTHOR]

A semiclassical method to simulate the electronic absorption and emission spectra of Br2 in an Ar matrix is presented. The appropriate time correlation functions are evaluated in the Condon approximation using Gaussian wave packet dynamics. Several approximate methods are used to propagate the wave packet and their relative merits in obtaining high resolution spectra are discussed. The dynamics using a single Gaussian wave packet is inadequate for obtaining spectra in highly anharmonic systems, frequently encountered in condensed phase problems. Where possible, the results of the simulation are compared in detail with available experiments. The simulated electronic absorption spectra confirm the physical picture advanced by Bondebey and Brus. It is shown that from the spectral analysis of the emission spectra one can infer some features of the guest–host interaction when the guest is in the electronically excited state. [ABSTRACT FROM AUTHOR]

We discuss whether or not local information on the potential energy surface embodied by the distribution of unstable instantaneous normal modes can be used to predict the hopping rates and barrier heights for Zwanzig's model of self-diffusion [R. Zwanzig, J. Chem. Phys. 79, 4507 (1983)] in simple liquids. Results from a set of simulations of Lennard-Jones particles done at multiple temperatures and densities are presented. These simulations show that the theories which predict diffusive barrier heights from the distribution of imaginary frequencies are questionable. This discrepancy is due to the presence of imaginary frequency instantaneous normal modes which persist into the solid phase. Model systems are used to show that imaginary frequency instantaneous normal modes (and even those at the top of the barrier along that mode) are not necessarily indicators of diffusive barrier crossing as used in Zwanzig's model. These false barriers are shown to be the cause of all of the imaginary frequency zero-force modes in the solid as well as many of the imaginary frequency modes in the high-density super-cooled liquid. We therefore dispute their utility as predictors of barrier heights or hopping rates in related liquid systems. We also show that attempts to separate the modes that are truly diffusive from those with false barriers using a frequency cutoff or local information on the potential energy surface are not successful at removing all of the non-barrier modes [ABSTRACT FROM AUTHOR]

A renormalization approach in quantum thermal annealing was applied to a highly frustrated BLN model protein with 46 residues. It enabled to achieve significant improvement in the success rate for locating the global minimum of this protein.