Spin-Pure Stochastic-CASSCF via GUGA-FCIQMC Applied to Iron–Sulfur Clusters

Dobrautz, Werner; Weser, Oskar; Bogdanov, Nikolay A.; Alavi, Ali; Manni, Giovanni Li

doi:10.1021/acs.jctc.1c00589

Cited by 45 publications

(125 citation statements)

References 170 publications

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“…[228,229] The energy spectrum of [4FeÀ 4S] was first explored with DMRG by Sharma et al, [230] followed by two appers of Li Manni et al using FCIQMC. [231,232] Even larger complexes, for example Nitrogenase cofactor FeMoco [MoFe 7 S 9 C], have been recently considered. [233,234] To summarize, we have shown many recent applications of accurate ab initio methods on metalloproteins containing not only one metal center but also multiple metal centers.…”

Section: Spin State Energetics In Metalloproteinsmentioning

confidence: 99%

Ab Initio Methods in First‐Row Transition Metal Chemistry

Feldt

Phung

2022

Eur J Inorg Chem

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Molecules containing 3d transition metals (TMs) are usually associated with versatile reactivity, partly due to their complicated electronic structures involving multiple close‐lying spin states. An accurate description of different electronic states is notoriously difficult and still a challenge for computational methodologies. Density functional theory, although repeatedly shown to give less reliable results for near‐degeneracy problems, remains the workhorse to explore the reactivity of TM complexes. Ab initio wavefunction theory has been lagging behind due to its high computational cost. However, tremendous efforts have been put to improve their applicability over the past few years, particularly local coupled cluster and low‐scaling multireference methods. In this mini‐review, we highlight major advancements of these ab initio techniques and discuss their recent applications in the calculations of spin state energetics of first‐row TM complexes, ranging from spin crossover compounds and metalloproteins to biomimetic complexes capable of activating C−H bonds.

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Section: Spin State Energetics In Metalloproteinsmentioning

confidence: 99%

Ab Initio Methods in First‐Row Transition Metal Chemistry

Feldt

Phung

2022

Eur J Inorg Chem

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“… 1 − 16 In these approaches, Ŝ 2 symmetry is explicitly enforced, ensuring zero spin contamination, and enabling the targeting of any desired spin state. The Graphical Unitary group approach (GUGA) 17 − 26 is one such example of a fully spin-adapted approach, which was implemented within the stochastic full-CI quantum Monte Carlo (FCIQMC) 9 , 27 − 30 and the Stochastic-CASSCF 10 , 31 , 32 frameworks. Recently, we have discovered a strategy within GUGA that allows an unprecedented reduction of the multireference character (compression) 32 − 35 of ground- and excited-state wave functions and the unique possibility to perform state-specific optimizations of ground- and excited-state wave functions.…”

Section: Introductionmentioning

confidence: 99%

“… 34 , 35 These properties arise from a unique block-diagonal structure of the GUGA Hamiltonian matrix, even within the same spin-symmetry sector, that follows chemically/physically motivated molecular orbital transformations. 34 This strategy has been applied to exchange-coupled polynuclear transition metal clusters with a large number of localized open-shell orbitals 32 − 35 and to one-dimensional Heisenberg and Hubbard model Hamiltonians. 36 In the latter cases, a connection with the concept of alternancy symmetry can be envisioned.…”

Section: Introductionmentioning

confidence: 99%

Spin Purification in Full-CI Quantum Monte Carlo via a First-Order Penalty Approach

et al. 2022

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In this article, we demonstrate that a first-order spin penalty scheme can be efficiently applied to the Slater determinant based Full-CI Quantum Monte Carlo (FCIQMC) algorithm, as a practical route toward spin purification. Two crucial applications are presented to demonstrate the validity and robustness of this scheme: the 1 Δ g ← 3 Σ g vertical excitation in O 2 and key spin gaps in a [Mn 3 (IV) O 4 ] cluster. In the absence of a robust spin adaptation/purification technique, both applications would be unattainable by Slater determinant based ground state methods, with any starting wave function collapsing into the higher-spin ground state during the optimization. This strategy can be coupled to other algorithms that use the Slater determinant based FCIQMC algorithm as configuration interaction eigensolver, including the Stochastic Generalized Active Space, the similarity-transformed FCIQMC, the tailored-CC, and second-order perturbation theory approaches. Moreover, in contrast to the GUGA-FCIQMC technique, this strategy features both spin projection and total spin adaptation, making it appealing when solving anisotropic Hamiltonians. It also provides spin-resolved reduced density matrices, important for the investigation of spin-dependent properties in polynuclear transition metal clusters, such as the hyperfine-coupling constants.

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“…To obtain the ground state eigenvalue ẼB 0 [u] of a given TC Hamiltonian H[u] B , we use the recently developed similarity transformed full-configuration interaction quantum Monte Carlo (ST-FCIQMC) technique 15,27 which extends the original stochastic projection technique of FCIQMC [28][29][30][31][32][33][34][35] to a non-hermitian and threebody Hamiltonian. The FCIQMC parameters were 10 6 walkers, an initiator threshold of n init = 3 and a semistochastic space of N D = 1000.…”

Section: A Computational Detailsmentioning

confidence: 99%

Performance of a one-parameter correlation factor for transcorrelation: the Li-Ne total energies and ionization potentials

Dobrautz¹,

Cohen²,

Alavi³

et al. 2022

Preprint

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In this work we investigate the performance of a recently proposed transcorrelated (TC) approach based on a single-parameter correlation factor [JCP, 154, 8, 2021] for systems involving more than two electrons. The benefit of such an approach relies on its simplicity as efficient numerical-analytical schemes can be set up to compute the two-and three-body integrals occuring in the effective TC Hamiltonian. To obtain accurate ground state energies within a given basis set, the present TC scheme is coupled to the recently proposed TC-full configuration interaction quantum Monte Carlo method [JCP, 151, 6, 2019]. We report ground state total energies on the Li-Ne series, together with their first cations, computed in increasing large basis sets and compare to more elaborate correlation factors involving electron-electron-nucleus coordinates. Numerical results on the Li-Ne ionization potentials show that the use of the single-parameter correlation factor brings on average only a slightly lower accuracy (1.2 mH) in a triple-zeta quality basis set with respect to a more sophisticated correlation factor. However, already using a quadruple-zeta quality basis set yields results within chemical accuracy to complete basis set limit results when using this novel single-parameter correlation factor.

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Spin-Pure Stochastic-CASSCF via GUGA-FCIQMC Applied to Iron–Sulfur Clusters

Cited by 45 publications

References 170 publications

Ab Initio Methods in First‐Row Transition Metal Chemistry

Ab Initio Methods in First‐Row Transition Metal Chemistry

Spin Purification in Full-CI Quantum Monte Carlo via a First-Order Penalty Approach

Performance of a one-parameter correlation factor for transcorrelation: the Li-Ne total energies and ionization potentials

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