Two new classes of non-iterative coupled-cluster methods derived from the method of moments of coupled-cluster equations

Abstract

Two recently proposed classes of non-iterative coupled-cluster (CC) methods derived from the method of moments of CC equations (MMCC) are discussed. The first approach, termed MMCC/PT, combines the MMCC formalism with a simplified form of multi-reference perturbation theory. The second approach, which leads to completely renormalized (CR) CC methods employing the left eigenstates of the similarity-transformed Hamiltonian, such as CR-CCSD, exploits the recently developed biorthogonal formulation of the MMCC theory. Both approaches are capable of improving the results of standard CC and equation-of-motion CC (EOMCC) calculations for ground-state potential energy surfaces along bond breaking coordinates and excited states dominated by two-electron transitions with computer costs similar to those characterizing the popular (and failing) CCSD(T) approximation. The performance of the basic MMCC/PT and CR-CCSD approximations, in which non-iterative corrections due to triple excitations are added to the ground-state energies obtained with the CC singles and doubles (CCSD) approach, is illustrated by the results of calculations for the HF, F₂ and H₂O molecules. The improvements offered by these approaches in the excited-state calculations are illustrated by the results for the vertical excitation energies of the CH⁺ ion.

Acknowledgements

We dedicate this paper to Professor Andrzej J. Sadlej in celebration of his 65th birthday. The senior author (PP) would like to thank Professor Bogumił Jeziorski for inviting him to write a contribution for a special issue of Molecular Physics in honor of Professor Andrzej J. Sadlej. This work has been supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy (Grant No. DE-FG02-01ER15228, PP), the National Science Foundation (Grant No. CHE-0309517, PP), the National Science Foundation Graduate Research Fellowship (JRG), the Dissertation Completion Fellowship provided by Michigan State University (JRG), and the James L. Dye Endowed Fellowship (MDL). The calculations were performed on the computer systems provided by the High Performance Computing Center at Michigan State University. PP also acknowledges the support offered by the Invited Fellowship of the Japan Society for the Promotion of Science during his two-month tenure as Visiting Professor at Kyoto University and useful discussions with his host, Professor Hiroshi Nakatsuji.

Notes

†Also at Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA

Additional information

Notes on contributors

Piotr Piecuch†

†Also at Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA