J. Tinka Gammel

Ground and defect states in a two band model of halogen-bridged transition metal linear chain complexes

Abstract We consider a two-band discrete tight-binding Peierls-Hubbard model for an isolated chain of a halogen-bridged, mixed-valence, transition metal linear chain complex (MX chain), which includes as parameters the difference between metal (M) and halogen (X) on site affinities, ϵM − ϵX = 20, a distance dependence βM,X of the on-site energies, the M-X hopping integral t and its distance dependence α, and an effective M-X spring K. We investigate: (1) ground states as functions of the model parameters; and (2) excitations — kinks, polarons, bipolarons, and photoexcitations — and their corresponding intra-gap absorption features.

Correlations in a two band model of halogen-bridged transition metal linear chain complexes

Abstract We have studied the effects of correlations in a simple two-band discrete tight-binding Peierls-Hubbard model for MX chains using perturbation theory, Hartree-Fock and exact diagonalization for classical adiabatic phonons, and a variational approach for quantum phonons.

Dynamical conductivity in polyacetylene

Abstract To allow for direct comparison with experiment we calculate the conductivity due to phonons in polyacetylene using a multicomponent Hamiltonian. A single soliton on a discrete lattice modeled the photoexcited data, while heavily doped systems were modeled with continuum soliton and polaron-like lattices. We discuss the effect of the IR active Goldstone mode, the third bound mode, and the recently predicted IR acoustic modes on the photoexcited spectra. The differences in the IR spectra for heavily doped soliton and polaron-like lattices and the consequences on the proposed first order phase transition are also discussed.

The extended Peierls-Hubbard model: Off-diagonal terms

Abstract We investigate the effects of including “off-diagonal” terms-nearest-neighbor bond-bond repulsion ( W ) and bond-site repulsion ( X ) — in the extended Peierls-Hubbard model. As a specific illustration we study the ground state dimerization in the one-dimensional, half-filled-band models that have been widely applied to conjugated polymers such as trans -polyacetylene and related charge density wave systems.

Signatures of stripe phases in hole-doped La 2 NiO 4

We model nickelate-centered and oxygen-centered stripe phases in doped

Shockwave response of two carbon fiber-polymer composites to 50 GPa

{\mathrm{La}}_{2}{\mathrm{NiO}}_{4}

Extracting Infinite System Properties from Finite Size Clusters: 'Phase Randomization/Boundary Condition Averaging'

materials. We use an inhomogeneous Hartree-Fock and random-phase approximation approach including both electron-electron and electron-lattice (e-l) coupling for a layer of

Determination of interaction parameters in peierls-hubbard models describing finite polyenes and polyacetylene

{\mathrm{La}}_{2}{\mathrm{NiO}}_{4}.

Ultragap edge states in mixed halide chain solids

We find that whether the ground state after commensurate hole doping comprises Ni-centered or O-centered charge-localized stripes depends sensitively on the e-l interaction. With increasing e-l interaction strength, a continuous transition from an O-centered stripe phase to a Ni-centered one is found. Various low- and high-energy signatures of these two kinds of stripe phases are predicted, which can clearly distinguish them. These signatures reflect the strongly correlated spin-charge-lattice features in the vicinity of Ni-centered or O-centered stripe domains. The importance of e-l interaction for recent experiments on stripe phases is discussed.

MX chains: 1-D analog of CuD planes?

Shock compression of two molded, carbon fiber-filled polymer composites was performed in gas gun-driven plate impact experiments at impact velocities up to ≈5 km/s. Hugoniot states for both composites were obtained from <5 GPa to nearly 50 GPa. The two materials contained a high fill percentage of chopped carbon fibers, bound by either phenolic or cyanate ester polymeric resins. Their dynamic responses were similar, although the 10 wt. % difference of carbon fill produced measureable divergence in shock compressibility. The chopped carbon fibers in the polymer matrix led to moderately anisotropic shocks, particularly when compared with the more commonly encountered filament-wound carbon fiber-epoxy composites. A discontinuity, or cusp, was observed in the principal Hugoniot of both materials near 25 GPa. We attribute the accompanying volume collapse to shock-driven chemical decomposition above this condition. Inert and reacted products equations of state were used to capture the response of the two materi...