1,575 research outputs found

    Bridges—Mathematics Support for Third-Grade Girls

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    A Maximum Entropy Method of Obtaining Thermodynamic Properties from Quantum Monte Carlo Simulations

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    We describe a novel method to obtain thermodynamic properties of quantum systems using Baysian Inference -- Maximum Entropy techniques. The method is applicable to energy values sampled at a discrete set of temperatures from Quantum Monte Carlo Simulations. The internal energy and the specific heat of the system are easily obtained as are errorbars on these quantities. The entropy and the free energy are also obtainable. No assumptions as to the specific functional form of the energy are made. The use of a priori information, such as a sum rule on the entropy, is built into the method. As a non-trivial example of the method, we obtain the specific heat of the three-dimensional Periodic Anderson Model.Comment: 8 pages, 3 figure

    A novel FLEX supplemented QMC approach to the Hubbard model

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    This paper introduces a novel ansatz-based technique for solution of the Hubbard model over two length scales. Short range correlations are treated exactly using a dynamical cluster approximation QMC simulation, while longer-length-scale physics requiring larger cluster sizes is incorporated through the introduction of the fluctuation exchange (FLEX) approximation. The properties of the resulting hybrid scheme are examined, and the description of local moment formation is compared to exact results in 1D. The effects of electron-electron coupling and electron doping on the shape of the Fermi-surface are demonstrated in 2D. Causality is examined in both 1D and 2D. We find that the scheme is successful if QMC clusters of NC≥4N_C\ge 4 are used (with sufficiently high temperatures in 1D), however very small QMC clusters of NC=1N_C=1 lead to acausal results

    Transport Properties of the Infinite Dimensional Hubbard Model

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    Results for the optical conductivity and resistivity of the Hubbard model in infinite spatial dimensions are presented. At half filling we observe a gradual crossover from a normal Fermi-liquid with a Drude peak at ω=0\omega=0 in the optical conductivity to an insulator as a function of UU for temperatures above the antiferromagnetic phase transition. When doped, the ``insulator'' becomes a Fermi-liquid with a corresponding temperature dependence of the optical conductivity and resistivity. We find a T2T^2-coefficient in the low temperature resistivity which suggests that the carriers in the system acquire a considerable mass-enhancement due to the strong local correlations. At high temperatures, a crossover into a semi-metallic regime takes place.Comment: 14 page
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