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

0428099 - ÚFCH JH 2015 RIV US eng J - Journal Article
Nooijen, M. - Demel, Ondřej - Datta, D. - Kong, L. - Shamasundar, K. R. - Lotrich, V. - Huntington, L. M. - Neese, F.
Communication: Multireference equation of motion coupled cluster: A transform and diagonalize approach to electronic structure.
Journal of Chemical Physics. Roč. 140, č. 8 (2014), 081102. ISSN 0021-9606. E-ISSN 1089-7690
R&D Projects: GA ČR GPP208/10/P041; GA ČR GAP208/11/2222
Institutional support: RVO:61388955
Keywords : Electronic states * Electronic structure * Equations of motion
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 2.952, year: 2014

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-2-O-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.
Permanent Link: http://hdl.handle.net/11104/0233525