The coupled-cluster revolution

Abstract

The elements of coupled-cluster (CC) theory that distinguish it from other ways of treating the correlation problem are presented. These essential components required that new theory be developed to treat analytical gradients, excited states, higher order properties, and now multi-reference CC. Aided by these developments, CC theory provides the best answers for the largest number of problems in molecular structure and spectra. Many scientists who spent time at the Quantum Theory Project were instrumental in these developments.

Keywords:

• properties
• analytic gradients
• coupled-cluster theory
• excited states
• multireference CC

Acknowledgements

MANY very talented co-workers have joined us in the effort to develop CC theory. Most of them are listed in the citations, are co-authors of ACES I, II, or III, and several have contributed to this special issue to present their own commentary on certain developments. In alphabetical order, Ludwik Adamowicz, Kyoung Baeck, Anna Balkova, Maria Barysz, David Bernholdt, Ariana Beste, Sam Cole, Don Comeau, George Fitzgerald, Norbert Flocke, Jűrgen Gauss, Jan Geertsen, Irek Grabowski, Steve Gwaltney, Robert Harrison, Tom Henderson, Osama Hino, So Hirata, Tom Hughes, T. Kinoshita, Stanislaw Kucharski, Bill Laidig, Walt Lauderdale, Yoon Sup Lee, Victor Lotrich, Dmitry Lyahk, David Magers, Leszek Meissner, Monika Musial, Jozef Noga, Marcel Nooijen, Nevin Oliphant, Sourav Pal, Rene Peloquin-Mattie, Ajith Perera, Piotr Piecuch, Mikhail Pitonak, Jiri Pittner, George Purvis, Lynn Redmon, Magnus Rittby, Piotr Rozyckzo, Alan Salter, Hideo Sekino, Carlos Sosa, John Stanton, Peter Szalay, Andrew Taube, Gary Trucks, Miro Urban, John Watts, Marta Wloch, and Sohrab Zarrabian. There are also those who made many applications of our evolving methods to ‘real’ chemistry: George Adams, Richard Brown, Ivan Cernusak, Janet Del Bene, Afaf al Derzi, Stefan Fau, Kim Ferris, Jim Franz, Adriana Gregusova, Gennady Gutsev, Anatoli Korkin, Stacek Kwiatkowski, Tadeusz Pluta, Lynn Salemi, Ken Wilson, and for weak interactions, Krzysztof Szalewicz. There were many others whose research emphasis in my group was on polymers, materials modelling, integrals, or dynamics, but often added critical insight nonetheless. These included Paul Bracken, Y. Hsiao, Christine Jamorski, Josh McClellan, C. J. Mei, Rafal Podeszwa, Sonia Sekusak, Jun Sun, DeCarlos Taylor, Motoi Tobita, Takahashi Tsuchiya, and Stefan Varga. Those involved with ab initio dft are listed in another contribution to this issue. I thank all of them for their essential efforts that enabled them to overcome whatever handicaps I put in their way. I am quite proud of the ‘school’ of coupled-cluster theory that developed in QTP.

A special thank you goes to Ajith Perera, my graduate student, post doc, Research Scientist, and long-time colloborator. He has been the keeper of the ACES II program system, is now making important contributions to the massively parallel ACES III, and is one of the best chemists in our group. He has provided the continuity, asked the critical questions, and offered the computational know-how I lack. Without his efforts, we would have accomplished far less. I also thank the other ACES III developers, Erik Deumens, Mark Ponton, and Tom Watson, not mentioned above.

Considering the nature of this special issue, I would be remiss if I did not recognize the ‘crucible’ that was QTP, whose milieu was instrumental in our development of CC theory. Löwdin's emphasis on perturbation theory and the correlation problem, complemented by Õhrn's work with the ‘other many-body method’, propagators, formulated in second-quantized form, were esential parts of the foundation I acquired as a student, continued as a postdoc in Aarhus with Linderberg, and brought to fruition with our MBPT papers while at Hopkins (thanks to the freedom granted by Bob Parr), that continued at Battelle. It was a modest, but important step to CC from there; and George Purvis, also from QTP, was instrumental in making that step.

I also want to thank the AFOSR who had the foresight to support our MBPT and CC effort from 1977 to the present, without interuption. We owe the last several years to the kind oversight of Dr. Mike Berman.