Improving the calculation of magnetic coupling constants in MRPT methods

Spivak, Mariano; Angeli, Celestino; Calzado, Carmen J.; Graaf, Coen de

doi:10.1002/jcc.23672

Cited by 22 publications

(36 citation statements)

References 49 publications

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“…On the other hand, the ground‐state configuration of the free ion was 90% 8 S + 10% 6 P at SOC‐NEVPT2 with CAS(7,7) level of theory. The differences can be attributed to the limit of the NEVPT2 approach, which can miss about 15% to 30% of the dynamical correlation effects [ 9 ] (Table S2). It is important to note that four‐component multiconfiguration calculations also lack dynamical correlation.…”

Section: Resultsmentioning

confidence: 99%

Theoretical examination of covalency in berkelium(IV) carbonate complexes

Albrecht‐Schönzart

Hobart

Páez‐Hernández

et al. 2020

Int J of Quantum Chemistry

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Experimental studies on the speciation of berkelium in carbonate media have shown that complexation of berkelium(III) by carbonate results in spontaneous oxidation to berkelium(IV) and that multiple species can be present in solution. We studied two proposed structures present in solution based on theoretical comparisons with spectroscopic data previously reported for Bk(IV) carbonate solutions. The multiconfigurational character of the ground and low‐lying excited states in both complexes is demonstrated to result from the strong spin‐orbit coupling. Although bonding in Bk(IV) carbonate and carbonate‐hydroxide complexes is dominated by strong Coulombic forces, the presence of non‐negligible covalent character is supported by ligand‐field theory, natural localized orbitals, topological studies of the electron density, and energy transition state natural orbitals for chemical valence. Bond orders based on natural localized molecular orbitals show that BkOH bonds possess enhanced orbital overlap, which is reflected in the bond strength. This is also observed in the decomposition of the orbital interaction energy into individual deformation density pairs.

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Section: Resultsmentioning

confidence: 99%

Theoretical examination of covalency in berkelium(IV) carbonate complexes

Albrecht‐Schönzart

Hobart

Páez‐Hernández

et al. 2020

Int J of Quantum Chemistry

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“…In contrast, spin‐state‐averaged optimizations that included all states of the Heisenberg ladder produced a regular Landé spacing of magnetic levels, or at least drastically reduced the magnitude of these deviations – but this only if sufficiently high M values are employed (see Table ). Importantly, Spivak et al . also used state‐averaged orbitals in their study that concluded that deviations reported by Harris et al .…”

Section: Exchange‐coupled Systemsmentioning

confidence: 86%

“…The deviations from the isotropic bilinear HDvV Hamiltonian were modeled with the addition of a biquadratic term, which was larger for the chromium than for the iron system. It should be noted, however, that the need to invoke a biquadratic exchange term for the chromium complex was questioned in a subsequent study of the same system by Spivak et al., who found no indication of deviations from the bilinear HDvV model.…”

Section: Exchange‐coupled Systemsmentioning

confidence: 99%

“…A theoretically transparent ab initio methodology that has been used for small exchange coupling problems involves the creation of a minimal active space typically composed of the singly occupied metal orbitals, followed by multireference perturbational treatment, or better by a difference‐dedicated configuration interaction (DDCI) treatment that takes into account the required excitation classes relevant to the exchange coupling problem . However, this otherwise successful approach faces limitations in its scope of applicability arising from the explosive computational cost of DDCI.…”

Section: Exchange‐coupled Systemsmentioning

confidence: 99%

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Multireference Approaches to Spin‐State Energetics of Transition Metal Complexes Utilizing the Density Matrix Renormalization Group

Roemelt

Pantazis

2019

Advcd Theory and Sims

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The accurate and reliable calculation of different electronic states in transition metal systems is a persistent challenge for theoretical chemistry. The widespread use of density functional theory for computing the relative energies of states with different spin in transition metal complexes not only has not discouraged, but often, owing to its limitations, has motivated the development and refinement of first-principles wavefunction-based methods, including both single-reference and multireference approaches. A significant boost for the latter has been the emergence of the density matrix renormalization group (DMRG) as a reliable tool in applied quantum chemistry. By enabling the use of larger active spaces than conventionally possible, DMRG has opened up areas of transition metal chemistry that were previously inaccessible to multireference approaches. The present perspective provides an overview of representative studies that make use of DMRG methods and discusses recent applications to spin-state energetics of transition metal systems. These range from mononuclear to exchange-coupled systems that define an important emerging field of DMRG applications. Major achievements are highlighted and potential pitfalls are identified with a view toward future methodological developments as well as extensions in the applicability of DMRG-based approaches to problems of spin-state energetics and exchange-coupling in transition metal chemistry.

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“…Denn andernfalls -also bei Spinspezifischer Orbitaloptimierungwürden die einzelnen Spinzustände und ihre relativen Energien falsch berechnet. 12e,12g, 13) In einigen Fällen führt dies zu einer falschen Interpretation des Experiments.…”

Section: Multireferenzmethoden Nutzenunclassified

Magnetische Wechselwirkungen quantenchemisch charakterisieren, Trendbericht Theoretische Chemie 2020, Teil 2

Krewald¹

2020

Nachr Chem

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Magnetische Wechselwirkungen quantenchemisch charakterisieren Magnetische Kopplungen entstehen durch quantenmechanische Wechselwirkungen zwischen ungepaarten Elektronen in einem Molekül, einem Cluster oder einem ausgedehnten Festkörper. Die Quantenchemie ist daher das Werkzeug der Wahl, um magnetische Kopplungen zu verstehen. Bis heute bleibt die quantitative Beschreibung und Analyse allerdings eine Herausforderung. Sie ist nur mit methodischen und technischen Entwicklungen aus den letzten Jahren zu bewältigen. Konzepte der theoretischen Magnetochemie Bevor sich Moleküle, Cluster oder Festkörperausschnitte quantenchemisch beschreiben ließen, beschrieb man gemessene magnetische Wechselwirkungen mit phänomenologischen Hamilton-Operatoren. 1) Dabei wird jedem magnetisch aktiven Zentrum (i, j) ein Spin zu-gewiesen (Abbildung 1a). Die Spins koppeln mit der Stärke J ij miteinander. Aus dieser magnetischen Kopplung ergeben sich die Spinzustände des Gesamtsystems, die als Spinleiter mit Sprossen S min bis S max dargestellt werden. Den Abstand der Sprossen bestimmen die Kopplungsstärke J ij und der Gesamtspin an den magnetischen Zentren. Diesen Zusammenhang drückt der Heisenberg-Dirac-van-Vleck(HDvV)-Hamilton-Operator aus. Sind die Spins benachbarter Zentren parallel ausgerichtet, spricht man von ferromagnetischer Kopplung mit dem Grundzustand S max. Sind die Spins antiparallel ausgerichtet, liegt antiferromagnetische Kopplung vor, und die Spinleiter wird umgedreht, sodass S min der Grundzustand ist (Abbildung 1b). Bei mehreren magnetisch aktiven Zentren gibt es mehrere Kopplungskonstanten J ij , die unterschiedliche Vorzeichen und Stärken haben können (Abbildung 1c).

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Improving the calculation of magnetic coupling constants in MRPT methods

Cited by 22 publications

References 49 publications

Theoretical examination of covalency in berkelium(IV) carbonate complexes

Theoretical examination of covalency in berkelium(IV) carbonate complexes

Multireference Approaches to Spin‐State Energetics of Transition Metal Complexes Utilizing the Density Matrix Renormalization Group

Magnetische Wechselwirkungen quantenchemisch charakterisieren, Trendbericht Theoretische Chemie 2020, Teil 2

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