Density functional plus dynamical mean-field theory of the spin-crossover molecule<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mtext>Fe(phen)</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mtext>(NCS)</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:math>

Chen, Jia; Millis, Andrew J.; Marianetti, Chris A.

doi:10.1103/physrevb.91.241111

Cited by 55 publications

(55 citation statements)

References 61 publications

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“…This approach is equivalent to the full rotationally-invariant formalism by Liechtenstein et al 42 if the on-site exchange parameter J is set to 0, which can be justified by previous work indicating that SDFT already contains an intrinsic J. 34,43 We choose to use the single spin/orbitalindependent parameter U as opposed to using the full local Coulomb interaction [see, for example, Ref. 44] for two reasons: (1) the spin-dependent portion of the density functional contains effects of on-site exchange 34,43 and we choose to proceed at this level of theory, and (2) a large portion of the DFT+U literature has taken this same approach.…”

Section: Methodology a Dft+u Approach For Correlated Materialsmentioning

confidence: 99%

“…34,43 We choose to use the single spin/orbitalindependent parameter U as opposed to using the full local Coulomb interaction [see, for example, Ref. 44] for two reasons: (1) the spin-dependent portion of the density functional contains effects of on-site exchange 34,43 and we choose to proceed at this level of theory, and (2) a large portion of the DFT+U literature has taken this same approach. Additionally, although in principle U is a function of the local environment and valence of the transition metal, in this work we always use a single U value independent of ionic site as is common practice.…”

Section: Methodology a Dft+u Approach For Correlated Materialsmentioning

confidence: 99%

“…Since the DMFT impurity problem itself is a difficult (though tractable) many-body problem, one approach is to make further approximations and solve the DMFT impurity problem within the Hartree-Fock approximation, which results in the DFT+U approach. Alternatively, it may be possible to exactly solve the DMFT impurity problem using quantum Monte Carlo (QMC) techniques 48,49 , which can have a profound influence on the energetics as compared to DFT+U 43,50,51 . In particular, the error associated with DFT+U was shown to strongly depend on the spin state of Fe in a spin crossover molecule 43 , which may suggest that DFT+U errors will strongly depend on Li concentration in cathode materials and therefore affect phase stability and battery voltages.…”

Section: 45-47mentioning

confidence: 99%

“…Alternatively, it may be possible to exactly solve the DMFT impurity problem using quantum Monte Carlo (QMC) techniques 48,49 , which can have a profound influence on the energetics as compared to DFT+U 43,50,51 . In particular, the error associated with DFT+U was shown to strongly depend on the spin state of Fe in a spin crossover molecule 43 , which may suggest that DFT+U errors will strongly depend on Li concentration in cathode materials and therefore affect phase stability and battery voltages. The quality of DFT+DMFT (solved using QMC) is superior to DFT+U in every sense, but the former is far more computationally expensive and complex.…”

Section: 45-47mentioning

confidence: 99%

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Compositional phase stability of strongly correlated electron materials within DFT+ U

Isaacs

Marianetti

2017

Phys. Rev. B

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Predicting the compositional phase stability of strongly correlated electron materials is an outstanding challenge in condensed matter physics. In this work, we employ the density functional theory plus U (DFT+U ) formalism to address the effects of local correlations due to transition metal d electrons on compositional phase stability in the prototype phase stable and separating materials LixCoO2 and olivine LixFePO4, respectively. We exploit a new spectral decomposition of the DFT+U total energy, revealing the distinct roles of the filling and ordering of the d orbital correlated subspace. The on-site interaction U drives both of these very different materials systems towards phase separation, stemming from enhanced ordering of the d orbital occupancies in the x = 0 and x = 1 species, whereas changes in the overall filling of the d shell contribute negligibly. We show that DFT+U formation energies are qualitatively consistent with experiments for phase stable LixCoO2, phase separating LixFePO4, and phase stable LixCoPO4. However, we find that charge ordering plays a critical role in the energetics at intermediate x, strongly dampening the tendency for the Hubbard U to drive phase separation. Most relevantly, the phase stability of Li 1/2 CoO2 within DFT+U is qualitatively incorrect without allowing charge ordering, which is problematic given that neither charge ordering nor the band gap that it induces are observed in experiment. We demonstrate that charge ordering arises from the correlated subspace interaction energy as opposed to the double counting. Additionally, we predict the Li order-disorder transition temperature for Li 1/2 CoO2, demonstrating that the unphysical charge ordering within DFT+U renders the method problematic, often producing unrealistically large results. Our findings motivate the need for other advanced techniques, such as DFT plus dynamical mean-field theory, for total energies in strongly correlated materials.

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Section: Methodology a Dft+u Approach For Correlated Materialsmentioning

confidence: 99%

Section: Methodology a Dft+u Approach For Correlated Materialsmentioning

confidence: 99%

Section: 45-47mentioning

confidence: 99%

Section: 45-47mentioning

confidence: 99%

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Compositional phase stability of strongly correlated electron materials within DFT+ U

Isaacs

Marianetti

2017

Phys. Rev. B

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“…1) has been chosen as a complex that is most suitable to test the methods described above. It certainly is one of the most intensively studied SCO complex and also one of the very few that have been studied by periodic DFT calculations [12,[19][20][21][22][23][24]. High precision crystal structures are available for the HS and LS phases at different temperatures down to 15 K [25,26].…”

Section: Ising-like Modelsmentioning

confidence: 99%

Cooperativity of Spin Crossover Complexes: Combining Periodic Density Functional Calculations and Monte Carlo Simulations

Kreutzburg

Hübner

Paulsen

2017

Preprint

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Abstract:The total enthalpies of the 16 different spin configurations that can be realized in the unit cell of the archetype spin crossover complex [Fe(phen) 2 (NCS) 2 ] (phen=1,2-phenanthroline) were calculated applying periodic density functional theory combined with the Hubbard model and the Grimme-D2 dispersion correction (DFT+U/D2). The obtained enthalpy differences between the individual spin configurations were used to determine spin couplings of an Ising-like model and subsequent Monte Carlo simulations for this model allowed to estimate the phenomenological interaction parameter Γ of the Slichter-Drickamer model, which is commonly used to describe the cooperativity of the spin transition. The calculational procedure described here, which led to an estimate of about 3 kJ mol −1 for Γ, in good agreement with experiment, may be used to predict from first principles how modifications of spin crossover complexes can change the character of the spin transition from gradual to abrupt and vice versa.

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Quantum embedding electronic structure methods

Wasserman

Pavanello

2020

Int J of Quantum Chemistry

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This editorial serves as an introduction to a series of 10 papers collected under the special issue "Quantum Embedding Electronic Structure Methods." The idea to assemble a special issue came during a symposium at the Spring 2019 meeting of the American Chemical Society where we (Adam and Michele) organized a Physical Chemistry symposium bearing the same name as the special issue. The symposium ran for the entire week and featured many flavors of embedding: from density embedding to embedding within lattice models, as well as continuum models and many-body expansions. While it may seem that these approaches are far removed from each other, the symposium highlighted common goals, such as the reduction of the computational effort through "divide-and-conquer" strategies, and stressed the importance of establishing a common language across all embedding methods. It is clear that human interaction is key for scientific progress, and traveling to conferences is an important aspect of scientific research. Unfortunately, we write this introduction during a pandemic of historic proportions, when working on theoretical and computational chemistry may seem like an unacceptable luxury or an unjustified distraction. It is striking to remember how we interacted prior to the outbreak. Figure 1 provides a glimpse into the social nature of the symposium participants and the massive crowds at the conference. The editorial is organized into three sections: Origins, where we briefly discuss the origins of embedding methods for newcomers to the field; Present, where we highlight some of the current efforts with an emphasis on the contributions submitted to this Special Issue of IJQC; and Future, where we enumerate a few of the open challenges in the field and speculate on some of its possible future directions. 2 | ORIGINS Modern embedding methods can be broadly classified into three groups: density embedding, density-matrix and Green's function (GF) embedding, and classical (quantum mechanics / molecular mechanics (QM/MM) and continuum dielectrics) embedding. We briefly discuss the origins of these three approaches separately. orbitals. The KSCED follows by requiring that E[n] be minimized directly with regard to variations of the n α (r). A different set of equations is

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Density functional plus dynamical mean-field theory of the spin-crossover moleculeFe(phen)2(NCS)2

Cited by 55 publications

References 61 publications

Compositional phase stability of strongly correlated electron materials within DFT+ U

Compositional phase stability of strongly correlated electron materials within DFT+ U

Cooperativity of Spin Crossover Complexes: Combining Periodic Density Functional Calculations and Monte Carlo Simulations

Quantum embedding electronic structure methods

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