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Static Structure Factor (static + structure_factor)
Selected AbstractsTemperature and Pressure Effects on Local Structure and Chain Packing in cis -1,4-Polybutadiene from Detailed Molecular Dynamics SimulationsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2006Georgia Tsolou Abstract Summary: We present results for the temperature and pressure dependence of local structure and chain packing in cis -1,4-polybutadiene (cis -1,4-PB) from detailed molecular dynamics (MD) simulations with a united-atom model. The simulations have been executed in the NPT statistical ensemble with a parallel, multiple time step MD algorithm, which allowed us to access simulation times up to 1 µs. Because of this, a 32 chain C128cis -1,4-PB system was successfully simulated over a wide range of temperature (from 430 to 195 K) and pressure (from 1 atm to 3 kbar) conditions. Simulation predictions are reported for the temperature and pressure dependence of the: (a) density; (b) chain characteristic ratio, Cn; (c) intermolecular pair distribution function, g(r), static structure factor, S(q), and first peak position, Qmax, in the S(q) pattern; (d) free volume around each monomer unit along a chain for the simulated polymer system. These were thoroughly compared against available experimental data. One of the most important findings of this work is that the component of the S(q) vs. q plot representing intramolecular contributions in a fully deuterated cis -1,4-PB sample exhibits a monotonic decrease with q which remains completely unaffected by the pressure. In contrast, the intermolecular contribution exhibits a distinct peak (at around 1.4 Å,1) whose position shifts towards higher q values as the pressure is raised, accompanied by a decrease in its intensity. 3D view of the simulation box containing 32 chains of C128cis -1,4-polybutadiene at density ,,=,0.849 g,·,cm,3 and the conformation of a single C128cis -1,4-PB chain fully unwrapped in space. [source] Quasiparticle interference induced by a momentum-dependent scattering in an s-wave superconducting statePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2005P. Pisarski Abstract Fourier transformed maps of the local density of states in disordered superconducting Bi2Sr2CaCu2O8+, provided important information on the quasiparticle states and their interference in high-temperature superconductors. Neglecting the momentum-dependence of the impurity potential it is possible to disentangle the quasiparticle interference effect from the static structure factor of the scatterers. The k-dependence of the impurity potential makes such a distinction difficult. Here, for the model momentum-dependent potential, we discuss the quasiparticle interference induced by an impurity in an s-wave superconductor. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The high-density electron gas: How momentum distribution n (k) and static structure factor S(q) are mutually related through the off-shell self-energy , (k, ,)ANNALEN DER PHYSIK, Issue 10 2010P. Ziesche For the spin-unpolarized uniform electron gas, rigorous theorems are used (Migdal, Galitskii-Migdal, Hellmann-Feynman) which allow the calculation of the pair density, g(r), or equivalently its Fourier transform, the static structure factor, S(q), from the dynamical 1-body self-energy , (k, ,), supposing the self-energy is (approximately) known as a functional, depending on the kinetic energy of a single electron, t(k), and on the bare Coulomb repulsion between two electrons, v(q). With the momentum distribution, n(k), and with the kinetic (t) and potential (v) components of the total energy e = t + v, the respective steps are: (i) , (k, ,) , n(k) , t, (ii) , (k, ,) , v, (iii) t + v = e, S(q). How this general scheme works in detail is shown explicitly for the high-density limit (as an illustration). For this case the ring-diagram partial summation or random-phase approximation applies. In this way, the results of Macke (1950), Gell-Mann/Brueckner (1957), Daniel/Vosko (1960), Kulik (1961), and Kimball (1976) are summarized in a coherent manner. Besides, several identities were brought to the light, e.g. the Kimball function for S(q) proves to be identical with Macke's momentum transfer function I(q) for e. [source] Interacting bosons in an optical latticeANNALEN DER PHYSIK, Issue 8 2008C. Moseley Abstract A strongly interacting Bose gas in an optical lattice is studied using a hard-core interaction. Two different approaches are introduced, one is based on a spin-1/2 Fermi gas with attractive interaction, the other one on a functional integral with an additional constraint (slave-boson approach). The relation between fermions and hard-core bosons is briefly discussed for the case of a one-dimensional Bose gas. For a three-dimensional gas we identify the order parameter of the Bose-Einstein condensate through a Hubbard-Stratonovich transformation and treat the corresponding theories within a mean-field approximation and with Gaussian fluctuations. This allows us to evaluate the phase diagram, including the Bose-Einstein condensate and the Mott insulator, the density-density correlation function, the static structure factor, and the quasiparticle excitation spectrum. The role of quantum and thermal fluctuations are studied in detail for both approaches, where we find good agreement with the Gross-Pitaevskii equation and with the Bogoliubov approach in the dilute regime. In the dense regime, which is characterized by the phase transition between the Bose-Einstein condensate and the Mott insulator, we discuss a renormalized Gross-Pitaevskii equation. This equation can describe the macroscopic wave function of the Bose-Einstein condensate in the dilute regime as well as close to the transition to the Mott insulator. Finally, we compare the results of the attractive spin-1/2 Fermi gas and those of the slave-boson approach and find good agreement for all physical quantities. [source] | ||||||||||