Spin projection with double hybrid density functional theory

Thompson, Lee M.; Hratchian, Hrant P.

doi:10.1063/1.4887361

Cited by 22 publications

(22 citation statements)

References 28 publications

(25 reference statements)

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“…The idea of DH scheme can be traced back to the work of Ernzerhof which used by Zhao et al through the multi‐coefficient methods and finally popularized by Grimme, the author of the B2‐PLYP model. In recent years, a large number of DHs with variety of density functional approximations (DFAs) has been proposed and validated on different properties . We refer the interested reader to the recent review articles in the field of DH‐DFT …”

Section: Theoretical and Methodological Frameworkmentioning

confidence: 99%

Order of stabilities in water nanoclusters: Insight from some recent double‐hybrid functionals

Fallahzadeh

2016

Int J of Quantum Chemistry

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In the present work, the applicability of some of the recently proposed and modern double‐hybrid (DH) models and other density functional theory (DFT) approximations has been analyzed for a difficult test, the order of stability in low‐energy isomers of water nanoclusters. In particular, we aim to systematically investigate for these functionals the role played by several factors such as dispersion correction, integrand functions upon which the DHs are based, and different spin scaling for the perturbative term in DH calculations of the relative energies for various isomers of water nanoclusters (H2O)20. From the obtained results, the superior performance of DHs with respect to the functionals from previous rungs is confirmed. It is shown that the dispersion corrected DHs perform better than noncorrected counterparts. Plus, the DH models based on cubic integrand (CI) and quadratic integrand (QI) functions are nearly equivalent in performance. We also find that using only contributions of electron pairs with opposite spin for the perturbative correlation part through scaled opposite spin scheme does not represent a significant improvement on accuracy of the results. Putting all the results together, the dispersion corrected parameterized DHs and parameter‐free DH models involving CI and QI functions outperform other approximations for relative energies of water 20‐mers. Altogether, predicting the correct order of the stability in water nanoclusters may be considered as another Achilles' heel in DFT calculations, although more analyses in this context are still needed. © 2016 Wiley Periodicals, Inc.

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Section: Theoretical and Methodological Frameworkmentioning

confidence: 99%

Order of stabilities in water nanoclusters: Insight from some recent double‐hybrid functionals

Fallahzadeh

2016

Int J of Quantum Chemistry

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“…However, in practical terms, experience suggests that the approximate and more tractable form of S 2 obtained from the Kohn-Sham determinant is acceptable in the types of calculations being carried out here. 10,16 For each approximate density functional, three different geometries were used for calculating J-couplings. The first approach, and perhaps most widely used methodology in similar benchmark studies, determines the J value using published crystal structures.…”

Section: Computational Detailsmentioning

confidence: 99%

“…11 However, in the case of DFT approaches, such a claim is somewhat more tenuous due to the more complicated nature of the S 2 operator and inclusion of some degree of static correlation in many commonly used density functionals; although, many popular functionals exhibit similar numerical behavior to HF in molecular systems experiencing spin contamination from symmetry breaking. 8,16 Approximate Projection (AP), a PAV method proposed by Yamaguchi and coworkers, 17 and other related spin-decontamination models by Malrieu and coworkers [18][19][20][21] have been successfully used in energy calculations of transition metal complexes and organic diradicals. 10,22,23 In a particularly intriguing report, Malrieu and Trinquier studied the effect of spin contamination on broken-symmetry singlet states of organic diradicals using a method they developed that estimates the optimized geometry of a spin projected singlet using AP like models.…”

Section: Introductionmentioning

confidence: 99%

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model to Improve Density Functional Calculations

Sheng¹,

Thompson²,

Hratchian

2019

Preprint

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This work evaluates the quality of exchange coupling constant and spin crossover gap calculations using density functional theory corrected by the Approximate Projection model. Results show that improvements using the Approximate Projection model range from modest to significant. This study demonstrates that, at least for the class of systems examined here, spin-projection generally improves the quality of density functional theory calculations of $J$-coupling constants and spin crossover gaps. Furthermore, it is shown that spin-projection can be important for both geometry optimization and energy evaluations. The Approximate Projection model provides an affordable and practical approach for effectively correcting spin-contamination errors in such calculations.

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“…Note that this form is computationally much more tractable than Löwin's spinprojection operator, 34 which has been extensively used in quantum chemistry for decades. [43][44][45][46][47] Applying Eq. (2) to a broken-symmetry UHF wave function, and minimizing its energy variationally, we obtain the so-called variation-after-projection (VAP) solution.…”

Section: B Spin-projection Modelmentioning

confidence: 99%

Spin-flip configuration interaction singles with exact spin-projection: Theory and applications to strongly correlated systems

Tsuchimochi

2015

The Journal of Chemical Physics

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Spin-flip approaches capture static correlation with the same computational scaling as the ordinary single reference methods. Here, we extend spin-flip configuration interaction singles (SFCIS) by projecting out intrinsic spin-contamination to make it spin-complete, rather than by explicitly complementing it with spin-coupled configurations. We give a general formalism of spin-projection for SFCIS, applicable to any spin states. The proposed method is viewed as a natural unification of SFCIS and spin-projected CIS to achieve a better qualitative accuracy at a low computational cost. While our wave function ansatz is more compact than previously proposed spin-complete SF approaches, it successfully offers more general static correlation beyond biradicals without sacrificing good quantum numbers. It is also shown that our method is invariant with respect to open-shell orbital rotations, due to the uniqueness of spin-projection. We will report benchmark calculations to demonstrate its qualitative performance on strongly correlated systems, including conical intersections that appear both in ground-excited and excited-excited degeneracies.

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Spin projection with double hybrid density functional theory

Cited by 22 publications

References 28 publications

Order of stabilities in water nanoclusters: Insight from some recent double‐hybrid functionals

Order of stabilities in water nanoclusters: Insight from some recent double‐hybrid functionals

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model to Improve Density Functional Calculations

Spin-flip configuration interaction singles with exact spin-projection: Theory and applications to strongly correlated systems

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