Analytic gradients for restricted active space second-order perturbation theory (RASPT2)

Nishimoto, Yoshio

doi:10.1063/5.0050074

Cited by 24 publications

(33 citation statements)

References 67 publications

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“…[134] Finally, we note that another (minor) problem of multireference perturbation theory for TM chemistry applications is the high cost of analytical gradients. Although CASPT2 (and NEVPT2) analytical gradients have been available for several years, [135][136][137][138][139][140] most studies currently employed structures obtained at the DFT level of theory or from crystallographic data. We are aware of only one systematic study on the performance of CASPT2 in the description of TM complex geometries.…”

Section: Multireference Configuration Interaction and Second-order Mu...mentioning

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: Multireference Configuration Interaction and Second-order Mu...mentioning

confidence: 99%

Ab Initio Methods in First‐Row Transition Metal Chemistry

Feldt

Phung

2022

Eur J Inorg Chem

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“…Not only is our method transferable to other levels of theory, which makes it a highly versatile tool, but the LVC approach can be systematically improved and extended to higher order couplings by, respectively, including higher excited state or higher order vibronic coupling parameters [43]. This opens doors for the highly anticipated augmentation of the current CASSCF treatment of spin-phonon coupling with dynamic correlation via multireference perturbation theory such as Complete Active Space 2nd order Perturbation Theory (CASPT2) [44][45][46], which has not been amenable to numerical differentiation schemes due to the presence of PES discontinuities.…”

Section: Discussionmentioning

confidence: 99%

An analytic linear vibronic coupling method for first-principles spin-dynamics calculations in single-molecule magnets

Staab

Chilton

2022

Preprint

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The accurate modeling of vibronically driven magnetic relaxation from ab initio calculations is of paramount importance to the design of next generation single-molecule magnets (SMMs). Previous theoretical studies have been relying on numerical differentiation to obtain spin-phonon couplings in the form of derivatives of spin Hamiltonian parameters. In this work, we introduce a novel approach to obtain these derivatives fully analytically by combining the linear vibronic coupling (LVC) approach with analytic CASSCF derivatives and nonadiabatic couplings computed at a single equilibrium geometry and electronic structure. We apply our analytic approach to the computation of Orbach and Raman relaxation rates in a solvated bis-cyclobutadienyl Dy(III) sandwich complex, where the solution environment is modelled by electrostatic multipole expansions, and benchmark our findings against results obtained using conventional numerical derivatives and a fully electronic description of the whole system. Among the ghost, charge and charge+dipole representations, we find that the point charge model shows the best agreement with the reference calculation, but note that the main source of discrepancies observed in the magnetic relaxation rates originates from the approximate equilibrium electronic structure computed using the electrostatic environment models, rather than from the couplings. We demonstrate that our novel LVC approach exhibits high accuracy over a wide range of coupling strengths and enables computational savings due to its analytic, "single-shot'' nature. Evidently, this offers great potential for advancing the simulation of a wide range of vibronic coupling phenomena in magnetism and spectroscopy, ultimately aiding the design of high-performance SMMs.

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“…This is for instance typical in the calculation of vertical transition energies, where only one or a few states of the excitation manifold are plagued by ISPs, albeit imposing the use of the shift for all states. Furthermore, considering the current wide availability of analytic nuclear energy gradients for CASPT2, 15 , 16 , 20 , 21 , 25 , 26 exploration of the potential energy surfaces, especially in the excited states, 27 has become more common, requiring a robust approach that effectively avoids ISPs and that at the same time does not affect the qualitative description in regions of the PES where these are not present. In this context, the real level shift 23 is not an ideal solution, the reason for which the imaginary level shift 24 had been developed.…”

Section: Introductionmentioning

confidence: 99%

Regularized CASPT2: an Intruder-State-Free Approach

Battaglia

Fransén

Galván

et al. 2022

J. Chem. Theory Comput.

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In this work we present a new approach to fix the intruder-state problem (ISP) in CASPT2 based on σ p regularization. The resulting σ p -CASPT2 method is compared to previous techniques, namely, the real and imaginary level shifts, on a theoretical basis and by performing a series of systematic calculations. The analysis is focused on two aspects, the effectiveness of σ p -CASPT2 in removing the ISP and the sensitivity of the approach with respect to the input parameter. We found that σ p -CASPT2 compares favorably with respect to previous approaches and that different versions, σ 1 -CASPT2 and σ 2 -CASPT2, have different potential application domains. This analysis also reveals the unsuitability of the real level shift technique as a general way to avoid the intruder-state problem.

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Analytic gradients for restricted active space second-order perturbation theory (RASPT2)

Cited by 24 publications

References 67 publications

Ab Initio Methods in First‐Row Transition Metal Chemistry

Ab Initio Methods in First‐Row Transition Metal Chemistry

An analytic linear vibronic coupling method for first-principles spin-dynamics calculations in single-molecule magnets

Regularized CASPT2: an Intruder-State-Free Approach

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