Enlarged symmetry groups of finite-size clusters with periodic noundary conditions

Any system that approximates an infinite lattice by a family of finite clusters (with periodic boundary conditions) passes through an intermediate region with enlarged (hidden) symmetry as the system size is increased. The hidden symmetry allows for extra degeneracies and level crossings and has application to exact-diagonalization studies, Monte Carlo simulations, lattice gauge theories, and renormalization group calculations.     

Localized exciton-phonon complex as an intermediate state in light scattering

A $\text{sharp}$ LO-phonon replica of the first order Raman spectrum of (Ga_xIn_1-xP and Ga(As_1-xP_x) has been observed for the first time. The experiment shows strong resonance with varying incoming photon energy which only appears in the presence of alloying and disorder. The results can only be understood if the relevant resonant intermediate state is a localized sharp exciton strongly interacting with the LO-phonon system, i.e. a localized exciton-phonon complex. Under those conditions, a simple model yields a ratio of the two-phonon to one-phonon intensities which is given by straightforward Franck-Condon overlaps.     

Model calculation of binding energies for multihole copper centers in germanium

Multihole binding energies of copper centers in germanium are calculated within a pseudoatom variational scheme in which a Heine-Abarenkov-type model potential is used as the impurity potential. Screening the hole-hole interaction by a position-dependent dielectric function is found to be crucial in understanding the observed multihole binding energies.     

Rapid crack growth in a thermoelastic solid under mixed-mode thermomechanical loading

A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed.     

Theory of n to π* transitions: more than tone nonbonding center

We extend the theory of n to π* transitions, previously developed, to include two or more nonbonding centers. When tunneling between nonbonding orbitals is taken into account the situation reduces to the familiar polymer (or specifically, dimer, for two nonbonding sites) vibronic problem with the n states playing the role of the polymer electronic states and the π electrons, the role of the polymer nuclear vibrations. A model calculation is presented for the -NN-group (attached to a non-conjugated system).