Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session B3: Few Body Nuclear Physics I |
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Sponsoring Units: DNP GFB Chair: Robert Wiringa, Argonne National Laboratory Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), St. Louis E |
Saturday, April 12, 2008 10:45AM - 11:21AM |
B3.00001: Auxiliary Field Diffusion Monte Carlo for nuclei and nuclear matter. Invited Speaker: Quantum Monte Carlo methods have become a mainstream tool for understanding many-body quantum systems. The nuclear Hamiltonian with its strong spin-isospin dependence presents some special difficulties. I will describe the Auxiliary Field Diffusion Monte Carlo method which combines diffusion Monte Carlo sampling of the spatial positions of the nucleons along with an auxiliary field breakup that simplifies the sampling of the spin-isospin degrees of freedom. Results for nuclei, nuclear and neutron matter will be shown. The current state of the calculations, the approximations being made, and future prospects will be discussed. [Preview Abstract] |
Saturday, April 12, 2008 11:21AM - 11:57AM |
B3.00002: Coupled-Cluster Theory for Molecular Structure and Spectra: The Challenges Posed By Molecules and the Coupled-Cluster Solutions Invited Speaker: Coupled-cluster (CC) theory derives from the ansatz that the n-particle wavefunction is $\vert \Psi >$=exp(T)$\vert $0$>$, where T is an excitation operator with $\vert $0$>$ some choice of mean-field wavefunction. That is sufficient to obtain energies. But to obtain anything else, we use the CC functional, E=$<$0$\vert $(!+$\Lambda )$exp(-T)Hexp(T)$\vert $0$>$, whose left and right hand eigenvectors provide energies and associated density matrices for the treatment of properties in CC theory. The introduction of $\Lambda $ makes it possible to obtain the $\sim $3N forces associated with N atoms in the same time as the energy itself. This is essential information for indentifying the critical points on a potential energy surface and their associated Hessians, for either the prediction of vibrational spectra or to characterize a saddle point (transition state) for a reaction. A generalization of the functional to $\omega $(k) =$<$0$\vert $L(k) exp(-T)Hexp(T)R(k)$\vert $0$>$, provides excitation energies, $\omega $(k) along with excited state left- and right-hand wavefunctions, Finally, with the response functions obtained from these left- and right-hand eigenfunctions, used in closed form, higher-order properties like NMR coupling constants are obtained. In this way, coupled-cluster theory provides a method that addresses all the properties of interest for molecules and their interactions. This development will be the topic of our contribution. For details please see, R. J. Bartlett and M Musial, ``Coupled-cluster theory in quantum chemistry'', Revs. of Modern Phys. \textbf{79, }291-352 (2007). [Preview Abstract] |
Saturday, April 12, 2008 11:57AM - 12:33PM |
B3.00003: Beyond the Shell Model: Computing Nuclei with Coupled-Cluster Theory Invited Speaker: Investigations of rare isotopes in the laboratory are opening the way to understand and clarify the properties of all nuclei and bulk nuclear matter. In this talk I will assess where we stand today in solving the nuclear problem and how future rare isotope facilities will impact our understanding of nuclei. The first part of the nuclear problem concerns our ability to describe complex nuclei using as input the basic interactions among protons and neutrons. Indeed, our community is on the verge of discovering how light nuclear systems are built from nuclear interactions that have their roots in QCD. I will describe this exciting frontier of research through illustrating recent progress in the nuclear implementation of coupled-cluster methods, a quantum many-body technique that enjoys great success in quantum chemistry. Nuclei offer some interesting challenges to coupled-cluster theory and quantum many-body theory generally: first, effective field theory implementations of the nuclear forces indicate the presence of a three-body force. Second, very weakly bound nuclei can best be described utilizing a single-particle basis consisting of bound and continuum states. In both cases, we have developed methods to solve for nuclear properties in these systems. I will also describe the computational requirements for the solution of the nuclear coupled-cluster problem. This research is supported by the U.S. Department of Energy under Contract Number DE-AC05-00OR22725 with UT-Battelle, LLC (Oak Ridge National Laboratory). [Preview Abstract] |
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