Coupled-cluster approaches with an approximate account of triexcitations and the optimized-inner-projection technique. II. Coupled-cluster results for cyclic-polyene model systems

Piecuch, Piotr; Zarrabian, Sohrab; Paldus, Josef; Čı́žek, J.

doi:10.1103/physrevb.42.3351

Cited by 80 publications

(74 citation statements)

References 107 publications

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“…The correlation energies for these values of p were obtained using Eqs. (20) and (36) these results are in agreement with those presented in [17].…”

Section: Results and Concluding Remarkssupporting

confidence: 95%

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Quasispin symmetry for the derivation of coupled cluster equations for the Hubbard model of benzene

Vinette

1992

Int J of Quantum Chemistry

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The concept of quasispin is applied to a special case of the Pariser-Parr-Pople (PPP) model of the benzene molecule, namely, the Hubbard Hamiltonian. Added to the spin, space, and alternancy symmetries already taken into account in the PPP Hamiltonian, this new symmetry, called quasispin symmetry, has the effect of reducing the size of the CI matrix. Coupled cluster (cc) equations are then obtained after applying the cc approach with doubles as well as its extension that accounts for triexcited clusters (ccsm-1). The derivation of these equations following the use of quasispin to the Hubbard model of benzene constitutes the most simple nontrivial example of cc results. In addition, the cc equations can be written in explicit algebraic form using the symbolic computation language MAPLE.

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“…The correlation energies for these values of p were obtained using Eqs. (20) and (36) these results are in agreement with those presented in [17].…”

Section: Results and Concluding Remarkssupporting

confidence: 95%

“…Indeed, constructing simultaneous eigenfunctions of spin and quasispin, as well as ob- %om [14]. 'From [17].…”

Section: Results and Concluding Remarksmentioning

confidence: 99%

Quasispin symmetry for the derivation of coupled cluster equations for the Hubbard model of benzene

Vinette

1992

Int J of Quantum Chemistry

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“…(See also [251].) The method was also successfully extended to include triples perturbationally (ACPTQ or ACCD + ST (ACCD) [231,249]). Of course, the perturbative account of triple corrections breaks down when we are far away from the equilibrium, just as with the usual CCSD(T) or CCSD[T] approaches.…”

Section: 3mentioning

confidence: 97%

A Critical Assessment of Coupled Cluster Method in Quantum Chemistry

Paldus

1999

Advances in Chemical Physics

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336

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“…)|RHF ) and taking advantage of this structure, perhaps in combination with the factorized form of the operators T n obtained from PHF wave functions, to obtain accurate results for strongly correlated systems at the cost of a well-defined wave function. [18,[34][35][36] Most of this work to date has focused on merging SUHF and coupled cluster in some way, but it could be generalized to the SGHF case.…”

Section: Discussionmentioning

confidence: 99%

Spin-projected generalized Hartree-Fock method as a polynomial of particle-hole excitations

Henderson

Scuseria

2017

Phys. Rev. A

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The past several years have seen renewed interest in the use of symmetry-projected HartreeFock for the description of strong correlations. Unfortunately, these symmetry-projected mean-field methods do not adequately account for dynamic correlation. Presumably, this shortcoming could be addressed if one could combine symmetry-projected Hartree-Fock with a many-body method such as coupled cluster theory, but this is by no means straightforward because the two techniques are formulated in very different ways. However, we have recently shown that the singlet S 2 -projected unrestricted Hartree-Fock wave function can in fact be written in a coupled cluster-like wave function: that is, the spin-projected unrestricted Hartree-Fock wave function can be written as a polynomial of a double-excitation operator acting on some closed-shell reference determinant. Here, we extend this result and show that the spin-projected generalized Hartree-Fock wave function (which has both S 2 and Sz projection) is likewise a polynomial of low-order excitation operators acting on a closed-shell determinant, and provide a closed-form expression for the resulting polynomial coefficients. The spin projection of the generalized Hartree-Fock wave function introduces connected triple and quadruple excitations which are absent when spin-projecting an unrestricted Hartree-Fock determinant. We include a few preliminary applications of the combination of this spin-projected Hartree-Fock and coupled cluster theory to the Hubbard Hamiltonian, and comment on generalizations of the methodology. Results here are not for production level, but a similarity-transformed theory that combines the two offers the promise of being accurate for both weak and strong correlation, and may offer significant improvements in the intermediate correlation regime where neither projected Hartree-Fock nor coupled cluster is particularly accurate.

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Coupled-cluster approaches with an approximate account of triexcitations and the optimized-inner-projection technique. II. Coupled-cluster results for cyclic-polyene model systems

Cited by 80 publications

References 107 publications

Quasispin symmetry for the derivation of coupled cluster equations for the Hubbard model of benzene

Quasispin symmetry for the derivation of coupled cluster equations for the Hubbard model of benzene

A Critical Assessment of Coupled Cluster Method in Quantum Chemistry

Spin-projected generalized Hartree-Fock method as a polynomial of particle-hole excitations

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