CASSCF version of density functional theory

Nakata, Kazuto; Ukai, Tomofumi; Yamanaka, Shusuke; Takada, Toshikazu; Yamaguchi, Kizashi

doi:10.1002/qua.21151

Cited by 19 publications

(15 citation statements)

References 63 publications

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“…47,48 While WFT-in-DFT methods aim at a multiscale description of large systems, MC-PDFT as well as sr-DFT-lr-WFT methods pursue similar objectives as DFT/MRCI. In the beginning, the combinations of generalized valence bond theory in perfect-pairing approximation 57,58 or minimal CASSCF or CASCI with DFT [59][60][61][62][63][64] were mostly thought to provide a proper description of bond dissociation processes in the electronic ground state. Later approaches used larger active spaces and additionally addressed electronically excited states [65][66][67][68][69] or strived for correcting the long-range behavior of TDDFT in describing CT states.…”

Section: Alternative Approachesmentioning

confidence: 99%

The DFT/MRCI method

Marian

Heil

Kleinschmidt

2018

WIREs Comput Mol Sci

148

154

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In the past two decades, the combined density functional theory and multireference configuration interaction (DFT/MRCI) method has developed from a powerful approach for computing spectral properties of singlet and triplet excited states of large molecules into a more general multireference method applicable to states of all spin multiplicities. In its original formulation, it shows great efficiency in the evaluation of singlet and triplet excited states which mainly originate from local one-electron transitions. Moreover, DFT/MRCI is one of the few methods applicable to large systems that yields the correct ordering of states in extended π-systems where double excitations play a significant role. A recently redesigned DFT/MRCI Hamiltonian extends the application range of the method to bichromophores such as hydrogen-bonded or π-stacked dimers and loosely coupled donor-acceptor systems. In conjunction with a restricted-open shell Kohn-Sham optimization of the molecular orbitals, even electronically excited doublet and quartet states can be addressed. After a short outline of the general ideas behind this semi-empirical method and a brief review of alternative approaches combining density functional and multireference wavefunction theory, formulae for the DFT/MRCI Hamiltonian matrix elements are presented and the adjustments of the two-electron contributions are discussed. The performance of the DFT/MRCI variants on excitation energies of organic molecules and transition metal compounds against experimental or ab initio reference data is analyzed and case studies are presented which show the strengths and limitations of the method. Finally, an overview over the properties available from DFT/MRCI wavefunctions and further developments is given.ABBREVIATIONS: ACRXTN, 3-(9,9-dimethylacridin-10[9H]-yl)-9H-xanthen-9-one; AO, atomic orbital; CASSCF, Complete active space self-consistent field; CASPT2, Complete active space second-order perturbation theory; CCSD(T), Coupled-cluster with singles and doubles and perturbative treatment of triples; CC2, Coupled-cluster with approximate treatment of doubles; CD, Circular dichroism; CI, Configuration interaction; CIPSI, configuration interaction by perturbation with multiconfigurational zeroth-order wave functions selected by iterative

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Section: Alternative Approachesmentioning

confidence: 99%

The DFT/MRCI method

Marian

Heil

Kleinschmidt

2018

WIREs Comput Mol Sci

148

154

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“…In fact, the hybrid DFT has been successfully applied to elucidate electronic structure of metalloenzymes, as shown in other series of our papers 13. The symmetry‐adapted (SA) CASDFT computations 18 of the potential curves for hydroxylation reactions by P450 are in progress in our laboratory.…”

Section: Theoretical Backgroundsmentioning

confidence: 90%

Extended Hartree–Fock theory of chemical reactions. VIII. Hydroxylation reactions by P450

Isobe

Nishihara

Yamanaka

et al. 2008

Int J of Quantum Chemistry

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ABSTRACT:We have investigated the reaction pathways for the primary hydroxylation reaction of trimethylmethane by a high-valent Fe(IV)AO porphyrincation radical species known as compound I at the B3LYP/CEP-31G level. The isoelectronic analogy of the Fe(IV)AO core of compound I to a molecular oxygen (O 2 ) has been successfully used to clarify the important roles of the singlet excited state of the Fe(IV)AO core in the alkane hydroxylation, which has hitherto been neglected. The reaction is initiated by the rate-determining hydrogen-atom abstraction from the substrate to give a discrete radical intermediate complex, in accordance with the conventional radical rebound mechanism. Similar to the chemistry of O 2 , however, one of the singlet excited states, i.e., the diradical component of the 1 ⌬ state of the Fe(IV)AO core intercepts the triplet ground state (the 3 ⌺ state) in the region of the transition state for the hydrogen abstraction. Our findings strongly indicate that the exchange polarization or intersystem crossing for the nonradiative transition to the locally singlet state is highly important to enhance the reactivity of compound I.

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“…On the other hand, the application of standard Density Functional Theory (DFT) methods to these (poly)radical systems is known to be affected by some pitfalls and/or artifacts: the intrinsic one-determinantal nature of Kohn–Sham (KS) DFT precludes dealing with orbital degeneracies, thus neglecting nondynamical or static correlation effects, and the use of a Broken-Symmetry (BS) solution for open-shell systems introduces spin-contamination (also scaling with size) issues mostly affecting the energy of the low-spin solution . This situation has historically prompted the development of nonstandard methods that are able to cope with these subtle electronic effects, namely, based on the two-body on-top pair density − with a revisited interest nowadays, − the balanced coupling of ab initio and density functional expressions, − the use of natural orbitals, − or the specific ensemble of pure spin states, − to name just a few of the existing nonstandard methods. Another possible route is the use of fractional spin or orbital occupation, , mimicking the situation when multiconfigurational ab initio methods are instead employed, or spin-flip techniques, − describing target states from a high-spin reference state.…”

Section: Introductionmentioning

confidence: 99%

Investigating the (Poly)Radicaloid Nature of Real-World Organic Compounds with DFT-Based Methods

et al. 2020

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Recent advances in the synthesis of stable organic (open-shell) polyradicaloids have opened their application as active compounds for emerging technologies. These systems typically exhibit small energy differences between states with different spin multiplicities, which are intrinsically difficult to calculate by theoretical methods. We thus apply here some DFT-based variants (FT-DFT, SF-DFT, and SF-TDDFT) on a test set of large and real-world molecules, as test systems for which such energy differences are experimentally available, also comparing systematically with RAS-SF results to infer if shortcomings of previous DFT applications are corrected. Additionally, we explore the spin-spin contribution to the ZFS tensor, of high interest for EPR spectroscopy, and derive the spatial extent of the corresponding (photoexcited) triplet state.

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CASSCF version of density functional theory

Cited by 19 publications

References 63 publications

The DFT/MRCI method

The DFT/MRCI method

Extended Hartree–Fock theory of chemical reactions. VIII. Hydroxylation reactions by P450

Investigating the (Poly)Radicaloid Nature of Real-World Organic Compounds with DFT-Based Methods

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