A state-specific multi-reference coupled cluster formalism with molecular applications

Mahapatra, Uttam Sinha; Datta, B. P.; Mukherjee, Debashis

doi:10.1080/002689798168448

Cited by 205 publications

(101 citation statements)

References 67 publications

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“…[1][2][3] To this same category belong several other MRCC approaches including methods based on the Jeziorski-Monkhorst ansatz 4 that have recently been thoroughly investigated. [5][6][7][8][9][10][11][12][13] However, the ic-MRCC approach presents two major advantages over the Jeziorski-Monkhorst methods: (i) in applications based on a complete-active-space (CAS) reference, the energy is fully invariant with respect to separate rotations among core, active, and virtual orbitals, 14 and (ii) the computational and memory costs scale formally with a leading term of the same order as the one of single-reference coupled cluster theory. 15 Benchmark ic-MRCC computations at the singles and doubles level (ic-MRCCSD) demonstrate compaa) Electronic mail: francesco.evangelista@yale.edu.…”

Section: Introductionmentioning

confidence: 99%

A sequential transformation approach to the internally contracted multireference coupled cluster method

Evangelista

Hanauer

Köhn

et al. 2012

The Journal of Chemical Physics

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The internally contracted multireference coupled cluster (ic-MRCC) approach is formulated using a new wave function ansatz based on a sequential transformation of the reference function (sqic-MRCC). This alternative wave function simplifies the formulation of computationally viable methods while preserving the accuracy of the ic-MRCC approach. The structure of the sqic-MRCC wave function allows folding the effect of the single excitations into a similarity-transformed Hamiltonian whose particle rank is equal to the one of the Hamiltonian. Consequently, we formulate an approximation to the sqic-MRCC method with singles and doubles (included respectively up to fourfold and twofold commutators, sqic-MRCCSD[2]) that contains all terms present in the corresponding single-reference coupled cluster scheme. Computations of the potential energy curves for the dissociation of BeH(2) show that the untruncated sqic-MRCCSD scheme yields results that are almost indistinguishable from the ordinary ic-MRCCSD method. The energy obtained from the computationally less expensive sqic-MRCCSD[2] approximation is found to deviate from the full ic-MRCCSD method by less than 0.2 mE(h) for BeH(2), while, in the case of water, the harmonic vibrational frequencies of ozone, the singlet-triplet splitting of p-benzyne, and the dissociation curve of N(2), sqic-MRCCSD[2] faithfully reproduces the results obtained via the ic-MRCCSD scheme truncated to two commutators. A formal proof is given of the equivalence of the ic-MRCC and sqic-MRCC methods with the internally contracted and full configuration interaction approaches.

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Section: Introductionmentioning

confidence: 99%

A sequential transformation approach to the internally contracted multireference coupled cluster method

Evangelista

Hanauer

Köhn

et al. 2012

The Journal of Chemical Physics

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“…In more demanding situations, when the single reference picture is no longer valid-a situation commonly identified with bond forming or bond breaking processes ͑resorting to more complicated state-universal or state-specific multireference CC approaches [12][13][14][15][16][17][18][19][20][21][22][23][24][25] is then recommended͒, practically all MBPT driven approaches fail. While in the single reference framework, it turned out that more sophisticated methodologies going beyond the conventional MBPT need to be used with the purpose of overcoming these difficulties.…”

Section: Introductionmentioning

confidence: 98%

Generating functionals based formulation of the method of moments of coupled cluster equations

Kowalski

Fan

2009

The Journal of Chemical Physics

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New theoretical framework for the method of moments of coupled cluster equations (MMCC) [K. Kowalski and P. Piecuch, J. Chem. Phys. 113, 18 (2000)] that, in a natural way, assures the connected form of the resulting MMCC corrections is discussed. In order to maintain the validity of the proposed expansion in the presence of strong quasidegeneracy effects, the regularization of the correlated part (gamma) of the overlap between the exact and approximate coupled cluster wave functions is required. It is shown that related approximations accounting for the effect of triples require a rudimentary form of the gamma-regularization (based on the regularization of cluster amplitudes) in order to provide results of completely renormalized CCSD(T) or better quality in situations when a single bond is broken (the HF molecule). For strongly correlated systems (C(2)) more efficient regularization schemes are required especially for stretched internuclear distances. Discussed type of the regularization procedure can also prevent the unphysical propagation of strong correlation effects through the products of cluster operators toward highly excited sectors of the Hilbert space.

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“…Attempts to fix this have led to the State-Specific (SS) MR-CC formulations, the BW [9] and Mk variant [10]. This in simplest terms is a kind of partitioning of the multi-state SU problem into trying to extract only one state at a time.…”

Section: New Philosophy For Mutlireference Coupled-cluster Theorymentioning

confidence: 99%

“…There are at least a half-dozen serious attempts in this direction that go under names like Fock Space, valence universal (VU) [5,6], Hilbert space, state universal(SU) [7,8], Hilbert space state specific (SS) [9,10], etc. but all have formal and computational limitations.…”

Section: Nature Of Mupreference Problemmentioning

confidence: 99%

Coupled Cluster Methods for Multi-Reference Applications

Bartlett¹,

Ponton²

2011

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A state-specific multi-reference coupled cluster formalism with molecular applications

Cited by 205 publications

References 67 publications

A sequential transformation approach to the internally contracted multireference coupled cluster method

A sequential transformation approach to the internally contracted multireference coupled cluster method

Generating functionals based formulation of the method of moments of coupled cluster equations

Coupled Cluster Methods for Multi-Reference Applications

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