We report preliminary large scale ab initio calculations of ground and excited states of 16O using quantum chemistry inspired coupled cluster methods and realistic two-body interactions. By using the renormalized Hamiltonians obtained with a no-core G-matrix approach, we obtain the virtually converged results at the level of two-body interactions. Due to the polynomial scaling with the system size that characterizes coupled cluster methods, we can probe large model spaces with up to seven major oscillator shells, for which standard non-truncated shell-model calculations are not possible.

1 aPiecuch, Piotr1 aWloch, M.1 aDean, D., J.1 aGour, J., R1 aHjorth-Jensen}, M., {1 aPapenbrock, T.1 aKowalski, K. uhttps://icer.msu.edu/ab-initio-coupled-cluster-calculations-nuclei-using-methods-quantum-chemistry00864nas a2200193 4500008004100000245003800041210003800079300001400117490000700131520031100138653006000449100001900509700001700528700001600545700001400561700002600575700001400601856005500615 2006 eng d00aCoupled Cluster Theory for Nuclei0 aCoupled Cluster Theory for Nuclei a5338-53450 v203 aThis presentation focuses on some of the recent developments in low-energy nuclear structure theory, with emphasis on applications of coupled-cluster theory. We report on results for ground and excited states in 4He and 16O, and about extensions of coupled-cluster theory to treat three-body forces.

10aNuclear structure; light nuclei; coupled-cluster theory1 aPapenbrock, T.1 aDean, D., J.1 aGour, J., R1 aHagen, G.1 aHjorth-Jensen}, M., {1 aWloch, M. uhttps://icer.msu.edu/coupled-cluster-theory-nuclei01833nas a2200181 4500008004100000245006500041210006400106260001100170300001300181490000700194520127600201100001901477700001601496700002601512700001401538700001701552856008201569 2006 eng d00aCoupled-Cluster Calculations for Valence Systems around 16 O0 aCoupledCluster Calculations for Valence Systems around 16 O c8/2006 a18 pages0 v743 aWe study the ground and low-lying excited states of 15O, 17O, 15N, and 17F using modern two-body nucleon-nucleon interactions and the suitably designed variants of the ab initio equation-of-motion coupled-cluster theory aimed at an accurate description of systems with valence particles and holes. A number of properties of 15O, 17O, 15N, and 17F, including ways the energies of ground and excited states of valence systems around 16O change as functions of the number of nucleons, are correctly reproduced by the equation-of-motion coupled-cluster calculations performed in up to eight major-oscillator shells. Certain disagreements with experiment are in part because of the degrees of freedom such as three-body interactions not accounted for in our effective two-body Hamiltonians. In particular, the calculated binding energies of 15O/15N and 17O/17F enable us to rationalize the discrepancy between the experimental and recently published [Phys. Rev. Lett. 94, 212501 (2005)] equation-of-motion coupled-cluster excitation energies for the Jπ=3- state of 16O. Our calculations demonstrate the feasibility of the equation-of-motion coupled-cluster methods to deal with valence systems around closed-shell nuclei and to provide results for systems beyond A=16.

1 aPiecuch, Piotr1 aGour, J., R1 aHjorth-Jensen}, M., {1 aWloch, M.1 aDean, D., J. uhttps://icer.msu.edu/coupled-cluster-calculations-valence-systems-around-16-o01855nas a2200181 4500008004100000245006400041210006300105260001200168300001100180490000700191520130200198100001601500700001901516700002601535700001401561700001701575856008101592 2006 eng d00aCoupled-cluster calculations for valence systems around O160 aCoupledcluster calculations for valence systems around O16 c08/2006 a0243100 v743 aWe study the ground and low-lying excited states of {15O,} {17O,} {15N,} and {17F} using modern two-body nucleon-nucleon interactions and the suitably designed variants of the ab initio equation-of-motion coupled-cluster theory aimed at an accurate description of systems with valence particles and holes. A number of properties of {15O,} {17O,} {15N,} and {17F,} including ways the energies of ground and excited states of valence systems around {16O} change as functions of the number of nucleons, are correctly reproduced by the equation-of-motion coupled-cluster calculations performed in up to eight major-oscillator shells. Certain disagreements with experiment are in part because of the degrees of freedom such as three-body interactions not accounted for in our effective two-body Hamiltonians. In particular, the calculated binding energies of {15O/15N} and {17O/17F} enable us to rationalize the discrepancy between the experimental and recently published {[Phys.} Rev. Lett. 94, 212501 (2005)] equation-of-motion coupled-cluster excitation energies for the Jπ=3- state of {16O.} Our calculations demonstrate the feasibility of the equation-of-motion coupled-cluster methods to deal with valence systems around closed-shell nuclei and to provide results for systems beyond A=16.

1 aGour, J., R1 aPiecuch, Piotr1 aHjorth-Jensen}, M., {1 aWloch, M.1 aDean, D., J. uhttps://icer.msu.edu/coupled-cluster-calculations-valence-systems-around-o1601260nas a2200205 4500008004100000245004300041210004200084260001200126300001100138490000700149520068900156100001500845700001700860700001600877700002600893700001700919700001900936700001600955856008300971 2005 eng d00aAb Initio Coupled-Cluster Study of 16O0 aAb Initio CoupledCluster Study of 16O c06/2005 a2125010 v943 aWe report converged results for the ground and excited states and matter density of 16O using realistic two-body nucleon-nucleon interactions and coupled-cluster methods and algorithms developed in quantum chemistry. Most of the binding is obtained with the coupled-cluster singles and doubles approach. Additional binding due to three-body clusters (triples) is minimal. The coupled-cluster method with singles and doubles provides a good description of the matter density, charge radius, charge form factor, and excited states of a one-particle, one-hole nature, but it cannot describe the first-excited 0+ state. Incorporation of triples has no effect on the latter finding.

1 aWłoch, M.1 aDean, D., J.1 aGour, J., R1 aHjorth-Jensen}, M., {1 aKowalski, K.1 aPapenbrock, T.1 aPiecuch, P. uhttps://icer.msu.edu/research/publications/ab-initio-coupled-cluster-study-16o01233nas a2200193 4500008004100000245004100041210004000082260001200122490000700134520068900141100001900830700001400849700001700863700001600880700002600896700001700922700001900939856008100958 2005 eng d00aAb Initio Coupled-Cluster Study of O0 aAb Initio CoupledCluster Study of O c06/20050 v943 aWe report converged results for the ground and excited states and matter density of 16O using realistic two-body nucleon-nucleon interactions and coupled-cluster methods and algorithms developed in quantum chemistry. Most of the binding is obtained with the coupled-cluster singles and doubles approach. Additional binding due to three-body clusters (triples) is minimal. The coupled-cluster method with singles and doubles provides a good description of the matter density, charge radius, charge form factor, and excited states of a one-particle, one-hole nature, but it cannot describe the first-excited 0+ state. Incorporation of triples has no effect on the latter finding.

1 aPiecuch, Piotr1 aWloch, M.1 aDean, D., J.1 aGour, J., R1 aHjorth-Jensen}, M., {1 aKowalski, K.1 aPapenbrock, T. uhttps://icer.msu.edu/research/publications/ab-initio-coupled-cluster-study-o02028nas a2200193 4500008004100000245012400041210006900165260005600234300001000290490000800300520128900308100001901597700001401616700001601630700001701646700002601663700001901689856012601708 2005 eng d00aBridging Quantum Chemistry and Nuclear Structure Theory: Coupled-Cluster Calculations for Closed- and Open-Shell Nuclei0 aBridging Quantum Chemistry and Nuclear Structure Theory CoupledC aMelville, NYbAmerican Institute of Physicsc7/2005 a28-450 v7773 aWe review basic elements of the single-reference coupled-cluster theory and discuss large scale ab initio calculations of ground and excited states of 15O, 16O, and 17O using coupled-cluster methods and algorithms developed in quantum chemistry. By using realistic two-body interactions and the renormalized form of the Hamiltonian obtained with a no-core G-matrix approach, we obtain the converged results for 16O and promising preliminary results for 15O and 17O at the level of two-body interactions. The calculated properties other than energies include matter density, charge radius, and charge form factor. The relatively low costs of coupled-cluster calculations, which are characterized by the low-order polynomial scaling with the system size, enable us to probe large model spaces with up to 7 or 8 major oscillator shells, for which non-truncated shell-model calculations for nuclei with A = 15 17 active particles are presently not possible. We argue that the use of coupled-cluster methods and computer algorithms developed by quantum chemists to calculate properties of nuclei is an important step toward the development of accurate and affordable many-body theories that cross the boundaries of various physical sciences. ©2005 American Institute of Physics

1 aPiecuch, Piotr1 aWloch, M.1 aGour, J., R1 aDean, D., J.1 aHjorth-Jensen}, M., {1 aPapenbrock, T. uhttps://icer.msu.edu/bridging-quantum-chemistry-and-nuclear-structure-theory-coupled-cluster-calculations-closed-and-open01746nas a2200217 4500008004100000245008700041210006900128260001200197300001200209490000800221520103700229100001901266700001701285700001601302700001401318700002601332700001701358700001901375700001401394856012001408 2005 eng d00aNuclear Structure Calculations with Coupled-Cluster Methods from Quantum Chemistry0 aNuclear Structure Calculations with CoupledCluster Methods from c04/2005 a299-3080 v7523 aWe present several coupled-cluster calculations of ground and excited states of 4He and 16O employing methods from quantum chemistry. A comparison of coupled cluster results with the results of exact diagonalization of the hamiltonian in the same model space and other truncated shell-model calculations shows that the quantum chemistry inspired coupled cluster approximations provide an excellent description of ground and excited states of nuclei, with much less computational effort than traditional large-scale shell-model approaches. Unless truncations are made, for nuclei like 16O, full-fledged shell-model calculations with four or more major shells are not possible. However, these and even larger systems can be studied with the coupled cluster methods due to the polynomial rather than factorial scaling inherent in standard shell-model studies. This makes the coupled cluster approaches, developed in quantum chemistry, viable methods for describing weakly bound systems of interest for future nuclear facilities.

1 aPiecuch, Piotr1 aDean, D., J.1 aGour, J., R1 aHagen, G.1 aHjorth-Jensen}, M., {1 aKowalski, K.1 aPapenbrock, T.1 aWloch, M. uhttps://icer.msu.edu/research/publications/nuclear-structure-calculations-coupled-cluster-methods-quantum-chemistry