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Title: Communication: Multireference equation of motion coupled cluster: A transform and diagonalize approach to electronic structure

The novel multireference equation-of-motion coupled-cluster (MREOM-CC) approaches provide versatile and accurate access to a large number of electronic states. The methods proceed by a sequence of many-body similarity transformations and a subsequent diagonalization of the transformed Hamiltonian over a compact subspace. The transformed Hamiltonian is a connected entity and preserves spin- and spatial symmetry properties of the original Hamiltonian, but is no longer Hermitean. The final diagonalization spaces are defined in terms of a complete active space (CAS) and limited excitations (1h, 1p, 2h, …) out of the CAS. The methods are invariant to rotations of orbitals within their respective subspaces (inactive, active, external). Applications to first row transition metal atoms (Cr, Mn, and Fe) are presented yielding results for up to 524 electronic states (for Cr) with an rms error compared to experiment of about 0.05 eV. The accuracy of the MREOM family of methods is closely related to its favorable extensivity properties as illustrated by calculations on the O{sub 2}–O{sub 2} dimer. The computational costs of the transformation steps in MREOM are comparable to those of closed-shell Coupled Cluster Singles and Doubles (CCSD) approach.
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7]
  1. Department of Chemistry, University of Waterloo, Waterloo, N2L 3G1, Ontario (Canada)
  2. J. Heyrovský Institute of Physical Chemistry of AS CR v.v.i., Prague (Czech Republic)
  3. Institut for Physikalische Chemie, Johannes Gutenberg Universität, Mainz (Germany)
  4. Department of Chemistry, Stanford University, Stanford, California 94305 (United States)
  5. Department of Chemistry, Mohali University, IISER Mohali, Knowledge City, Sector 81, SAS Nagar, Manauli PO 140306 (India)
  6. Quantum Theory Project, University of Florida, Gainesville, Florida 32611-8435 (United States)
  7. Max Planck Institut für Chemische Energiekonversion, Mülheim an der Ruhr (Germany)
Publication Date:
OSTI Identifier:
22255037
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 8; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ACCURACY; DIMERS; ELECTRONIC STRUCTURE; EQUATIONS OF MOTION; EXCITATION; HAMILTONIANS; TRANSITION ELEMENTS