Highly efficient perturbative + variational strategy based on orthogonal valence bond theory for the evaluation of magnetic coupling constants. Application to the trinuclear Cu(<scp>ii</scp>) site of multicopper oxidases

Tenti, Lorenzo; Maynau, Daniel; Angeli, Celestino; Calzado, Carmen J.

doi:10.1039/c6cp03234f

Cited by 16 publications

(17 citation statements)

References 73 publications

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“…Disadvantages of BS-DFT include its inability to describe all individual spin states of the Heisenberg ladder and its lack of systematic improvability − With the impending facile accessibility of multiconfigurational descriptions for many oligonuclear systems with DMRG, − analytical tools are needed that connect the quantum-chemical description to established interpretations and chemical concepts. Other efforts in this direction are based on a Green’s-function approach that also allows a fragment-based analysis. , …”

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confidence: 99%

Orbital Entanglement Analysis of Exchange-Coupled Systems

Stein

Pantazis

Krewald

2019

J. Phys. Chem. Lett.

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A new tool for the interpretation of multiconfigurational wave functions representing the spin states of exchangecoupled transition metal complexes is introduced. Based on orbital entanglement measures, herein derived from multiconfigurational density matrix renormalization group calculations, the complexity of the wave function is reduced, thus facilitating a connection with established concepts for the interpretation of magnetically coupled systems. We show that the entanglement of localized orbitals with a small basis set is a good representation of the magnetic coupling topology and that it is sensitive to chemical changes in homologous complexes. Furthermore, we introduce a measure for the magnetic relevance of orbitals in the active subspace and a concept for the quantitative comparison of different chemical species. The approach presented here will be easily applicable to higher nuclearity clusters, providing a direct insight into all states of the Heisenberg spin ladder for systems previously accessible only by singleconfigurational methods.

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confidence: 99%

Orbital Entanglement Analysis of Exchange-Coupled Systems

Stein

Pantazis

Krewald

2019

J. Phys. Chem. Lett.

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“…It is important to mention the well-known over-delocalization of the DFT-based descriptions of the electronic structure, while CASSCF calculations are prone to overlocalize on the metal the singly occupied orbitals [42,43,44,45,46,47]. This manifests itself in the underestimation of the Cu 3d contribution at DFT level, and the overestimation at CASSCF one.…”

Section: Resultsmentioning

confidence: 99%

Light-Induced Control of the Spin Distribution on Cu–Dithiolene Complexes: A Correlated Ab Initio Study

Zapata-Rivera

Calzado

2019

Molecules

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Metal dithiolene complexes—M(dmit)2—are key building blocks for magnetic, conducting, and optical molecular materials, with singular electronic structures resulting from the mixing of the metal and dmit ligand orbitals. Their use in the design of magnetic and conducting materials is linked to the control of the unpaired electrons and their localized/delocalized nature. It has been recently found that UV–Vis light can control the spin distribution of some [Cu(dmit)2]−2 salts in a direct and reversible way. In this work, we study the optical response of these salts and the origin of the differences observed in the EPR spectra under UV–Vis irradiation by means of wave function-based quantum chemistry methods. The low-lying states of the complex have been characterized and the electronic transitions with a non-negligible oscillator strength have been identified. The population of the corresponding excited states promoted by the UV–Vis absorption produces significant changes in the spin distribution, and could explain the changes observed in the system upon illumination. The interaction between neighbor [Cu(dmit)2]−2 complexes is weakly ferromagnetic, consistent with the relative orientation of the magnetic orbitals and the crystal packing, but in disagreement with previous assignments. Our results put in evidence the complex electronic structure of the [Cu(dmit)2]−2 radical and the relevance of a multideterminantal approach for an adequate analysis of their properties.

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“…Description of states at CASSCF, MS-CASPT2, MRCI, and SAC-CI level of theory in terms of dominant electronic configurations (only the part differing from the GS or reference state is reported) with respect to the MOs depicted in Figure 2 (CASSCF/MS-CASPT2) or Figure 3 (5 %) view, such a procedure is called Orthogonal Valence Bond (OVB) reading of the CASSCF wavefunction [70] and has been used recently to explain and unravel the nature of complex wave functions. [71][72][73][74][75] The OVB name places this strategy in the frame of the orthogonal variant of the VB approach on the H 2 molecule. [76,77] Tables 7-9 report the most important electronic configurations for the first three states belonging to the A g irrep (those with a weight larger than 5 % for at least one of the three states), both in the CASSCF wave functions and for the wave functions obtained from the diagonalization of the effective Hamiltonian computed at the MS-CASPT2 (thus under the effect of electron dynamical correlation).…”

Section: An Analysis Of the Casscf Wavefunctions In Terms Of Localizementioning

confidence: 99%

The Intriguing Case of the One‐Photon and Two‐Photon Absorption of a Prototypical Symmetric Squaraine: Comparison of TDDFT and Wave‐Function Methods

et al. 2019

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We face the challenging description of the excited states responsible for one photon (OPA) and two photon (TPA) absorption in squaraine dyes, adopting both time-dependent density functional theory and a large variety of post Hartree Fock methods, including coupled cluster and adiabatic diagrammatic construction methods (ADC, to the second and third order), symmetry adapted cluster configuration interaction (CI), CASSCF including second-order perturbative corrections (PT2) with standard CASPT2 recipe and according to n-electron valence PT2 (NEVPT2) approach, and an additional multireference CI with PT2 corrections (CI-MRPT2). We selected a small prototypical symmetric squaraine dye for which these accurate computations are feasible and experimental data are available.We show that while all methods reasonably reproduce the OPA spectrum, an acceptable description and assignment of the states responsible for TPA is only possible through ADC(3) and multireference calculations, due to the strong involvement of double-excitations. The nature of ground state and OPA and TPA states is investigated with a rigorous reading of the CASSCF wavefunctions in terms of localized molecular orbitals on the donor and acceptor fragments, showing that these states arise from a balance of many different contributions including biradical configurations, local excitations and charge-transfer states where both side aromatic rings and the carbonyls of the squarylium moiety act as donors.[a] Dr.

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Highly efficient perturbative + variational strategy based on orthogonal valence bond theory for the evaluation of magnetic coupling constants. Application to the trinuclear Cu(ii) site of multicopper oxidases

Cited by 16 publications

References 73 publications

Orbital Entanglement Analysis of Exchange-Coupled Systems

Orbital Entanglement Analysis of Exchange-Coupled Systems

Light-Induced Control of the Spin Distribution on Cu–Dithiolene Complexes: A Correlated Ab Initio Study

The Intriguing Case of the One‐Photon and Two‐Photon Absorption of a Prototypical Symmetric Squaraine: Comparison of TDDFT and Wave‐Function Methods

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