Molecular Magnets: Phenomenology and Theory

Pederson, Mark R.; Baruah, Tunna

doi:10.1002/9780470022184.hmm125

Cited by 8 publications

(8 citation statements)

References 55 publications

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“…Multi-metallic compounds are interesting for many applications. − The coupling between their spin centers can be modeled using the effective Hamiltonian from the Heisenberg–Dirac–Van Vleck model. − This invokes a magnetic coupling parameter, J ab , that couples the spins localized on the two centers a and b and characterizes the type and extent of coupling between them. By convention, a negative J indicates antiferromagnetic coupling, and a positive J indicates a ferromagnetic one.…”

Section: Applications and Discussionmentioning

confidence: 99%

Localized Active Space-State Interaction: a Multireference Method for Chemical Insight

Pandharkar

Hermes

Cramer

et al. 2022

J. Chem. Theory Comput.

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Multireference electronic structure methods, like the complete active space (CAS) self-consistent field model, have long been used to characterize chemically interesting processes. Important work has been done in recent years to develop modifications having a lower computational cost than CAS, but typically these methods offer no more chemical insight than that from the CAS solution being approximated. In this paper, we present the localized active space-state interaction (LASSI) method that can be used not only to lower the intrinsic cost of the multireference calculation but also to improve interpretability. The localized active space (LAS) approach utilizes the local nature of the electron−electron correlation to express a composite wave function as an antisymmetrized product of unentangled wave functions in local active subspaces. LASSI then uses these LAS states as a basis from which to express complete molecular wave functions. This not only makes the molecular wave function more compact but also permits flexibility in choosing those states to be included in the basis. Such selective inclusion of states translates to the selective inclusion of specific types of interactions, thereby allowing a quantitative analysis of these interactions. We demonstrate the use of LASSI to study charge migration and spin-flip excitations in multireference organic molecules. We also compute the J coupling parameter for a bimetallic compound using various LAS bases to construct the Hamiltonian to provide insights into the coupling mechanism.

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Section: Applications and Discussionmentioning

confidence: 99%

Localized Active Space-State Interaction: a Multireference Method for Chemical Insight

Pandharkar

Hermes

Cramer

et al. 2022

J. Chem. Theory Comput.

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“…A set of transition-metal ions: Fe 3+ , Fe 2+ , and Mn + . 4. A single-center iron-containing SMM derived from the structure from Ref.…”

Section: A Computational Detailsmentioning

confidence: 99%

“…The ability to model these properties computationally is a key prerequisite for the design of novel materials. For example, single-molecule magnets (SMMs), molecules with several unpaired electrons that have a highspin ground state in the absence of an applied magnetic field, [3][4][5] can be used as building blocks to create novel, light-weight, and tunable magnetic materials or as building blocks for quantum information storage and quantum computations. [6][7][8][9] The key challenge in realizing the full potential of SMMs is the ability to tune and control their magnetic behavior.…”

Section: Introductionmentioning

confidence: 99%

General framework for calculating spin–orbit couplings using spinless one-particle density matrices: Theory and application to the equation-of-motion coupled-cluster wave functions

Pokhilko

Epifanovsky

Krylov

2019

The Journal of Chemical Physics

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Standard implementations of nonrelativistic excited-state calculations compute only one component of spin multiplets (i.e., Ms = 0 triplets); however, matrix elements for all components are necessary for deriving spin-dependent experimental observables. Wigner-Eckart's theorem allows one to circumvent explicit calculations of all multiplet components. We generate all other spin-orbit matrix elements by applying Wigner-Eckart's theorem to a reduced one-particle transition density matrix computed for a single multiplet component. In addition to computational efficiency, this approach also resolves the phase issue arising within Born-Oppenheimer's separation of nuclear and electronic degrees of freedom. A general formalism and its application to the calculation of spin-orbit couplings using equation-of-motion coupledcluster wave functions are presented. The two-electron contributions are included via the mean-field spin-orbit treatment. Intrinsic issues of constructing spin-orbit mean-field operators for open-shell references are discussed, and a resolution is proposed. The method is benchmarked by using several radicals and diradicals. The merits of the approach are illustrated by a calculation of the barrier for spin inversion in a high-spin tris(pyrrolylmethyl)amine Fe(II) complex.

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“…Single-molecule magnets (SMMs) are of interest due to their potential use in high-density information storage, spintronics, and quantum computing [1][2][3][4][5]. Rational tuning of their ground-state spin, magnetic anisotropy, and magnetic exchange couplings is essential in the design of SMMs with desired magnetic behavior (i.e., ferromagnetic or antiferromagnetic, switchable, etc.)…”

Section: Introductionmentioning

confidence: 99%

Magnetic Exchange Interactions in Binuclear and Tetranuclear Iron (III) Complexes Described by Spin-Flip DFT and Heisenberg Effective Hamiltonians

Kotaru

Kähler

Alessio

et al. 2022

Preprint

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Low-energy spectra of single-molecule magnets (SMMs) are often described by Heisenberg Hamiltonians. Within this formalism, exchange interactions between magnetic centers determine the ground-state multiplicity and energy separation between the ground and excited states. In this contribution, we extract exchange coupling constants (J) for a set of iron (III) binuclear and tetranuclear complexes from all-electron calculations using non-collinear spin-flip time-dependent density functional theory (NC-SF-TDDFT). For 12 binuclear complexes with J-values ranging from -6 to -132 cm−1, our benchmark calculations using the short-range hybrid ωPBEh functional and 6-31G(d,p) basis set agree well with the experimentally derived values (mean absolute error of 4.7 cm−1). For the tetranuclear SMMs, the computed J constants are within 6 cm−1 from the experimentally derived values. We explore the range of applicability of the Heisenberg model by analyzing bonding patterns in these Fe(III) complexes using natural orbitals (NO), their occupations, and the number of effectively unpaired electrons. The results illustrate the efficiency of the spin-flip protocol for computing the exchange couplings and the utility of the NO analysis in assessing the validity of effective spin Hamiltonians.

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Molecular Magnets: Phenomenology and Theory

Cited by 8 publications

References 55 publications

Localized Active Space-State Interaction: a Multireference Method for Chemical Insight

Localized Active Space-State Interaction: a Multireference Method for Chemical Insight

General framework for calculating spin–orbit couplings using spinless one-particle density matrices: Theory and application to the equation-of-motion coupled-cluster wave functions

Magnetic Exchange Interactions in Binuclear and Tetranuclear Iron (III) Complexes Described by Spin-Flip DFT and Heisenberg Effective Hamiltonians

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