David Dean

Rodney Bartlett

Walter Johnson

Achim Schwenk

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Inge Dolan
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Symposium on "50 Years of Coupled Cluster Theory"

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Atomic, Chemical, and Nuclear Developments in Coupled Cluster Methods (INT-08-2a)

June 23 - July 25, 2008

One of the most promising ab initio microscopic theories that can potentially provide a highly accurate description of a variety of many-body physical systems, as small as atomic nuclei and as large as polyatomic molecules, as weakly bound as van der Waals molecules and as strongly bound as atomic nuclei, is coupled-cluster theory.

A systematic implementation of coupled-cluster theory for nuclei is underway. This effort utilizes the formalism of coupled-cluster developments in chemistry, but with both physical and computational twists inherent in the physics of nuclei. The nuclear problem requires as input an interaction that is less well understood than in the atomic and chemical cases and a close interaction between those who produce realistic nucleon-nucleon interactions and the many-body specialists is required. In light nuclear systems, some significant tests of interactions have been made with configuration-interaction and quantum Monte Carlo calculations. It would appear that a real three-body interaction is required to reliably predict nuclear properties. The introduction of three-body interactions into the coupled-cluster formalism constitutes one interesting discussion point for this program. A second point from nuclear physics involves efforts to utilize a single-particle basis that includes bound, continuum, and scattering states. The coupled-cluster problem then translates to a complex algorithm for weakly bound nuclei.

Recent significant advances in developing coupled-cluster theory have occurred in quantum chemistry. A variety of coupled-cluster methods for ground, excited, closed-shell, and open-shell, non-degenerate and quasi-degenerate states of atoms and molecules and molecular properties have been developed and coded, so that nowadays coupled-cluster methods are regarded by theoretical and experimental chemists as the best ab initio techniques for high-accuracy electronic structure calculations.

In atomic physics, Parity Non-conservation (PNC) effects are one interesting focus where a relativistic coupled-cluster method will play a key role. Various atomic isotope shifts and applications in fundamental symmetries are also being pursued. Other important developments include the proper CC treatment of QED effects.

The goals of this program are as follows:

  1. to bring together scientists from nuclear physics, quantum chemistry, and atomic physics, to discuss the current status of coupled-cluster efforts in these three fields;
  2. to identify and discuss new directions that may be of common interest to the three fields; and,
  3. to share common experiences in understanding and applying the coupled-cluster methods to various problems of interest.