Symmetry and broken symmetry in molecular orbital description of unstable molecules IV: comparison between single- and multi-reference computational results for antiaromtic molecules

Saitô, Tôru; Nishihara, Satomichi; Yamanaka, Shusuke; Kitagawa, Yasutaka; Kawakami, Takashi; Yamada, Satoru; Isobe, Hiroshi; Okumura, Mitsutaka; Yamaguchi, Kizashi

doi:10.1007/s00214-011-0941-9

Cited by 42 publications

(46 citation statements)

References 106 publications

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“…86. The geometry of cyclobutadiene was taken from the work of Saito et al 65 Trimethylene diradical · CH 2 CH 2 CH 2 · and octacene geometries were optimized using UB3LYP/6-31G(d) with GAUSSIAN 03 66 program. Figure 2 shows the structures of TMM, cyclobutadiene, and octacene.…”

Section: Computational Detailsmentioning

confidence: 99%

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Variational fractional-spin density-functional theory for diradicals

Peng¹,

Hu²,

Devarajan³

et al. 2012

The Journal of Chemical Physics

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Accurate computation of singlet-triplet energy gaps of diradicals remains a challenging problem in density-functional theory (DFT). In this work, we propose a variational extension of our previous work [D. H. Ess, E. R. Johnson, X. Q. Hu, and W. T. Yang, J. Phys. Chem. A 115, 76 (2011)], which applied fractional-spin density-functional theory (FS-DFT) to diradicals. The original FS-DFT approach assumed equal spin-orbital occupancies of 0.5 α-spin and 0.5 β-spin for the two degenerate, or nearly degenerate, frontier orbitals. In contrast, the variational approach (VFS-DFT) optimizes the total energy of a singlet diradical with respect to the frontier-orbital occupation numbers, based on a full configuration-interaction picture. It is found that the optimal occupation numbers are exactly 0.5 α-spin and 0.5 β-spin for diradicals such as O(2), where the frontier orbitals belong to the same multidimensional irreducible representation, and VFS-DFT reduces to FS-DFT for these cases. However, for diradicals where the frontier orbitals do not belong to the same irreducible representation, the optimal occupation numbers can vary between 0 and 1. Furthermore, analysis of CH(2) by VFS-DFT and FS-DFT captures the (1)A(1) and (1)B(1) states, respectively. Finally, because of the static correlation error in commonly used density functional approximations, both VFS-DFT and FS-DFT calculations significantly overestimate the singlet-triplet energy gaps for disjoint diradicals, such as cyclobutadiene, in which the frontier orbitals are confined to separate atomic centers.

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Section: Computational Detailsmentioning

confidence: 99%

“…37 The geometry of square cyclobutadiene is adapted from Ref. 65. The · CH 2 CH 2 CH 2 · geometry is optimized with UB3LYP/6-31G(d) in GAUSSIAN 03.…”

Section: Two Types Of Diradicalsmentioning

confidence: 99%

Variational fractional-spin density-functional theory for diradicals

Peng¹,

Hu²,

Devarajan³

et al. 2012

The Journal of Chemical Physics

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“…[17] Theg eometry optimizations of [Ni III 2 (dpema) 2 (O) 2 ] 2+ at the UDFT-D3 level were conducted using the crystal structure of 2 as the initial structure.W ec hoose the UPBE0-D3BJ/def2-TZVP model [18] on the basis of preliminary calculations using several exchange-correlation functionals with the smaller 6-311G* basis set (Supporting Information, Table S5). [20] As the computed orbital overlap between CMOs is far smaller than 1.0 (0.114), the d z 2 orbitals of those nickel cores do not have significant overlaps ( Figure 5). [19] Moreover,t he J value for [Ni II 2 (dpema) 2 (OH) 2 ] 2+ computed by this model is also in qualitative agreement with the experimental result (À105.2 vs. À58.8 cm À1 ).…”

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confidence: 95%

A Bis(μ‐oxido)dinickel(III) Complex with a Triplet Ground State

et al. 2018

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A bis(μ-oxido)dinickel(III) complex was synthesized and characterized by single crystal X-ray diffraction, resonance Raman, and ESI-mass measurements. Magnetic susceptibility measurements by SQUID and EPR spectroscopy reveal that the complex has a triplet ground state, which is unprecedented for high-valent metal (M) complexes with [M (μ-O) ] diamond core. DFT studies indicate ferromagnetic coupling of the nickel(III) centers. The complex exhibits hydrogen abstraction reactivity and oxygenation reactivity toward external substrates.

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“…More experimental work needs to be performed to fully characterize the structure and other properties of this system, including lowtemperature MCD experiments. In addition, high level WFT methods, like CASPT2 [35] and MR-CC [36,37,39,40], and the recently developed semi-empirical KS LC-DFT, KS LC gau -DFT, KS LC-DFT?LRD, and KS LC gau -DFT?LRD [34] or ab inito KS-DFT methods using multireference (MR) optimized effective potentials (OEPs) will allow one to get quantitative numbers. The numbers we have reported here at LDA KS-DFT level using a single reference (SR) configuration can only be expected to give qualitative accuracy.…”

Section: Discussionmentioning

confidence: 99%

“…Considering that single reference Hartree-Fock wave function theory (WFT) quantum mechanics and local density approximation (LDA) and even the generalized gradient approximation (GGA) KS-DFT do not have the accuracy required for the calculation of weak van der Waals-dispersion interactions/forces, both WFT and KS-DFT needed to be extended and even reformulated to be applied for the dispersion forces and interactions that are responsible for the stability of the noble gas dimers and stacked aromatics compounds. Within KS-DFT theory, the so-called dispersion correction has been used [34], while in WFT, the methods commonly used are WFT electron correlation, that are known as correlated methods such as complete active space perturbation theory (CASPT2) [35] or multi-reference couple cluster (MR-CC) methods [36][37][38][39][40]. These are two of the most accurate WFT methods which are able to quantitatively treat the types of interactions and forces responsible for the stability of the structures in supramolecular chemistry, physics, and materials science.…”

Section: Introductionmentioning

confidence: 99%