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Science: Excited States
    Wednesday July 18, 2012 1:15pm - 1:45pm @ King Arthur 3rd Floor

    Science: Excited States in Lattice QCD using the Stochastic LapH Method

    Abstract: A new method for computing the mass spectrum of excited baryons and mesons from the temporal correlations of quantum-field operators in quantum chromodynamics is described. The correlations are determined using Markov-chain Monte Carlo estimates of QCD path integrals formulated on an anisotropic space-time lattice. Access to the excited states of interest requires determinations of lower-lying multi-hadron state energies, necessitating the use of multi-hadron operators. Evaluating the correlations of such multi-hadron operators is difficult with standard methods. A new stochastic method of treating the low-lying modes of quark propagation which exploits a new procedure for spatially-smearing quark fields, known as Laplacian Heaviside smearing, makes such calculations possible for the first time. A new operator for studying glueballs, a hypothetical form of matter comprised predominantly of gluons, is also tested, and computing the mixing of this glueball operator with a quark-antiquark operator and multiple two-pion operators is shown to be feasible. 



    Type Science Track
    Session Titles Quantum Methods


Science: Benchmark Calculations
    Wednesday July 18, 2012 1:45pm - 2:15pm @ King Arthur 3rd Floor

    Science: Benchmark Calculations for Multi-Photon Ionization of the Hydrogen Molecule and the Hydrogen Molecular Ion by Short-Pulse Intense Laser Radiation

    Abstract: We provide an overview of our recent work on the implementation of the finite-element discrete-variable representation to study the interaction of a few-cycle intense laser pulse with the H$_2$ and H$_2^{\,+}$ molecules. The problem is formulated in prolate spheroidal coordinates, the ideal system for a diatomic molecule, and the time-dependent Schr\"odinger equation is solved on a space-time grid. The physical information is extracted by projecting the time-evolved solution to the appropriate field-free states of the problem.



    Type Science Track
    Session Titles Quantum Methods


Science: Electrostatic Screening


Science: Quantum Algorithms
    Wednesday July 18, 2012 2:45pm - 3:15pm @ King Arthur 3rd Floor

    Science: Quantum Algorithms for Predicting the Properties of Complex Materials

    Abstract: A central goal in computational materials science is to find efficient methods for solving the Kohn-Sham equation. The realization of this goal would allow one to predict materials properties such as phase stability, structure and optical and dielectric properties for a wide variety of materials. Typically, a solution of the Kohn-Sham equation requires computing a set of low-lying eigenpairs. Standard methods for computing such eigenpairs require two procedures: (a) maintaining the orthogonality of an approximation space, and (b) forming approximate eigenpairs with the Rayleigh-Ritz method. These two procedures scale cubically with the number of desired eigenpairs. Recently, we presented a method, applicable to any large Hermitian eigenproblem, by which the spectrum is partitioned among distinct groups of processors. This "divide and conquer" approach serves as a parallelization scheme at the level of the solver, making it compatible with existing schemes that parallelize at a physical level and at the level of primitive operations, e.g., matrix-vector multiplication. In addition, among all processor sets, the size of any approximation subspace is reduced, thereby reducing the cost of orthogonalization and the Rayleigh-Ritz method. We will address the key aspects of the algorithm, its implementation in real space, and demonstrate the accuracy of the algorithm by computing the electronic structure of some representative materials problems.



    Type Science Track
    Session Titles Quantum Methods
    Tags Software and Middleware


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