The restricted active space self-consistent-field method, implemented with a split graph unitary group approach

A multireference second-order perturbation theory using a restricted active space self-consistent field wave function as reference ͑RASPT2/RASSCF͒ is described. This model is particularly effective for cases where a chemical system requires a balanced orbital active space that is too large to be addressed by the complete active space self-consistent field model with or without second-order perturbation theory ͑CASPT2 or CASSCF, respectively͒. Rather than permitting all possible electronic configurations of the electrons in the active space to appear in the reference wave function, certain orbitals are sequestered into two subspaces that permit a maximum number of occupations or holes, respectively, in any given configuration, thereby reducing the total number of possible configurations. Subsequent second-order perturbation theory captures additional dynamical correlation effects. Applications of the theory to the electronic structure of complexes involved in the activation of molecular oxygen by mono-and binuclear copper complexes are presented. In the mononuclear case, RASPT2 and CASPT2 provide very similar results. In the binuclear cases, however, only RASPT2 proves quantitatively useful, owing to the very large size of the necessary active space.

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“…24,25 In this model, the active subspace is itself divided into three distinct regions: RAS1, RAS2, and RAS3 ͑see Fig. 1͒.…”

Section: B the Rasscf/raspt2 Methodsmentioning

confidence: 99%

The restricted active space followed by second-order perturbation theory method: Theory and application to the study of CuO2 and Cu2O2 systems

Malmqvist

Pierloot

Shahi

et al. 2008

The Journal of Chemical Physics

490

532

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“…Single and double excitations from the O R 2p x , 2p z , and O A 2p x , 2p y , 2p z orbitals were considered by applying the restricted active space (RAS) method [23]. We used CAS reference wave functions based on an active subspace including the O R 2p y and V 3d xy orbitals.…”

Section: Volume 89 Number 7 P H Y S I C a L R E V I E W L E T T E R Smentioning

confidence: 99%

Theoretical Characterization of the Ground and Optically Excited States ofα′−NaV2O5
Hozoi
¹
,
Vries
²
,
Oosten
³

et al. 2002
Phys. Rev. Lett.
28
1
29
0
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Theoretical characterization of the ground and optically excited states of alpha Hozoi, L.; de Vries, Alexander; van Oosten, A.B.; Broer, Ria; Cabrero, J.; de Graaf, Cornelis Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. The character of the ground and optically excited states was investigated by quantum chemical calculations. We propose a rung ground state with V 3d 1 xy -O 2p 1 y -V 3d 1 xy character, instead of the conventional picture of one unpaired electron shared by 2 V ions. The unpaired electron on O is low-spin coupled to the V d electrons and spin density is predicted to be localized on vanadium. The absorption peak at 0.9 eV is assigned to a state with similar orbital occupations but a different spin coupling scheme, resulting in spin density localized on the bridging oxygen.

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“…It is now possible to describe the correlation in the active orbitals for active spaces with up to 50 orbitals, to produce a multireference active space wavefunction |Ψ 0 ⟩ that is formally the sum of many determinants. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] In these cases, the remaining challenge is to efficiently describe the correlation outside of the active space, involving the external orbitals. We refer to this as the dynamic correlation problem in a multireference setting.…”

Section: Introductionmentioning

confidence: 99%

A transformed framework for dynamic correlation in multireference problems

Sokolov

Chan

2015

The Journal of Chemical Physics

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We describe how multireference dynamic correlation theories can be naturally obtained as singlereference correlation theories in a canonically transformed frame. Such canonically transformed correlation theories are very simple and involve identical expressions to their single-reference counterparts. The corresponding excitations involve quasiparticles rather than the bare particles of the system. High-order density matrices (or their approximations) and the numerical metric instabilities common to multireference correlation theories do not appear. As an example, we formulate the Bogoliubov canonically transformed version of second-order Møller-Plesset perturbation theory and demonstrate its performance in H 2 , H 2 O, N 2 , and BeH 2 bond dissociation. C 2015 AIP Publishing LLC. [http://dx

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The restricted active space self-consistent-field method, implemented with a split graph unitary group approach

Cited by 702 publications

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The restricted active space followed by second-order perturbation theory method: Theory and application to the study of CuO2 and Cu2O2 systems

The restricted active space followed by second-order perturbation theory method: Theory and application to the study of CuO2 and Cu2O2 systems

Theoretical Characterization of the Ground and Optically Excited States ofα′−NaV2O5
Hozoi
¹
,
Vries
²
,
Oosten
³

et al. 2002
Phys. Rev. Lett.
28
1
29
0
View full text Add to dashboard Cite

A transformed framework for dynamic correlation in multireference problems

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The restricted active space self-consistent-field method, implemented with a split graph unitary group approach

Cited by 702 publications

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The restricted active space followed by second-order perturbation theory method: Theory and application to the study of CuO2 and Cu2O2 systems

The restricted active space followed by second-order perturbation theory method: Theory and application to the study of CuO2 and Cu2O2 systems

Theoretical Characterization of the Ground and Optically Excited States ofα′−NaV2O5Hozoi1, Vries2, Oosten3 et al. 2002Phys. Rev. Lett.281290View full textAdd to dashboardCite

A transformed framework for dynamic correlation in multireference problems

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Theoretical Characterization of the Ground and Optically Excited States ofα′−NaV2O5
Hozoi
¹
,
Vries
²
,
Oosten
³

et al. 2002
Phys. Rev. Lett.
28
1
29
0
View full text Add to dashboard Cite