Ab initio computations of effective exchange integrals for H–H, H–He–H and Mn2O2 complex: comparison of broken-symmetry approaches

Soda, Tomohisa; Kitagawa, Yasutaka; Onishi, Taku; Takano, Yu; Shigeta, Yasuteru; Nagao, Hidemi; Yoshioka, Yasunori; Yamaguchi, Kizashi

doi:10.1016/s0009-2614(00)00166-4

Cited by 719 publications

(556 citation statements)

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“…The quoted coupling constants are based on formalism of Yamaguchi, which employs calculated expectation values S 2 for both high-spin and broken-symmetry states 34,35 . Calculations employed the PBE0 functional, which has previously been demonstrated to yield reliable values for magnetic couplings in analogous systems 21,36 .…”

Section: Calculations a Density Functional Theorymentioning

confidence: 99%

Control of the third dimension in copper-based square-lattice antiferromagnets

et al. 2016

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Using a mixed-ligand synthetic scheme, we create a family of quasi-two-dimensional antiferromagnets, namely, [Cu(HF2)(pyz)2]ClO4 [pyz = pyrazine], [CuL2(pyz)2](ClO4)2 [L = pyO = pyridine-N-oxide and 4-phpyO = 4-phenylpyridine-N-oxide. These materials are shown to possess equivalent two-dimensional [Cu(pyz)2] 2+ nearly square layers, but exhibit interlayer spacings that vary from 6.5713Å to 16.777Å, as dictated by the axial ligands. We present the structural and magnetic properties of this family as determined via x-ray diffraction, electron-spin resonance, pulsed-and quasistatic-field magnetometry and muon-spin rotation, and compare them to those of the prototypical two-dimensional magnetic polymer Cu(pyz)2(ClO4)2. We find that, within the limits of the experimental error, the two-dimensional, intralayer exchange coupling in our family of materials remains largely unaffected by the axial ligand substitution, while the observed magnetic ordering temperature (1.91 K for the material with the HF2 axial ligand, 1.70 K for the pyO and 1.63 K for the 4-phpyO) decreases slowly with increasing layer separation. Despite the structural motifs common to this family and Cu(pyz)2(ClO4)2, the latter has significantly stronger two-dimensional exchange interactions and hence a higher ordering temperature. We discuss these results, as well as the mechanisms that might drive the long-range order in these materials, in terms of departures from the ideal S = 1/2 two-dimensional square-lattice Heisenberg antiferromagnet. In particular, we find that both spin exchange anisotropy in the intralayer interaction and interlayer couplings (exchange, dipolar, or both) are needed to account for the observed ordering temperatures, with the intralayer anisotropy becoming more important as the layers are pulled further apart.

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Section: Calculations a Density Functional Theorymentioning

confidence: 99%

Control of the third dimension in copper-based square-lattice antiferromagnets

et al. 2016

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“…[46][47][48] The formalism of Yamaguchi, which employs calculated expectation values S 2 for both high-spin and brokensymmetry states, was used. 49,50 Calculations related to magnetic interactions have been performed using the PBE0 functional. The def2-TZVP basis function set from Ahlrichs was used.…”

Section: Experimental Methodsmentioning

confidence: 99%

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX₂(pyz)₂ (X = Cl, Br, I, NCS; pyz = Pyrazine)

et al. 2016

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Magnetism in a family of S = 1 square lattice antiferromagnets NiX 2 (pyz) 2 (X = Cl, Br, I, NCS; pyz = pyrazine) The crystal structures of NiX2(pyz)2 (X = Cl (1), Br (2), I (3) and NCS (4)) were determined at 298 K by synchrotron X-ray powder diffraction. All four compounds consist of two-dimensional (2D) square arrays self-assembled from octahedral NiN4X2 units that are bridged by pyz ligands. The 2D layered motifs displayed by 1-4 are relevant to bifluoride-bridged [Ni(HF2)(pyz)2]ZF6 (Z = P, Sb) which also possess the same 2D layers. In contrast, terminal X ligands occupy axial positions in 1-4 and cause a staggering of adjacent layers. Long-range antiferromagnetic order occurs below 1.5 (Cl), 1.9 (Br and NCS) and 2.5 K (I) as determined by heat capacity and muon-spin relaxation. The single-ion anisotropy and g factor of 2, 3 and 4 are measured by electron spin resonance where no zero-field splitting was found. The magnetism of 1-4 crosses a spectrum from quasi-two-dimensional to three-dimensional antiferromagnetism. An excellent agreement was found between the pulsedfield magnetization, magnetic susceptibility and TN of 2 and 4. Magnetization curves for 2 and 4 calculated by quantum Monte Carlo simulation also show excellent agreement with the pulsed-field data. 3 is characterized as a three-dimensional antiferromagnet with the interlayer interaction (J ⊥ ) slightly stronger than the interaction within the two-dimensional [Ni(pyz)2] 2+ square planes (Jpyz).

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“…If each spin is mainly localized on one site (a or b site), as illustrated in I of Fig. 3, we can estimate J ab values between magnetic sites on the basis of the Heisenberg model (Onishi et al, 2001;Salem, 1982;Soda et al, 2000;Takano et al, 2008;Takano et al, 2002a;Takano et al, 2001;Takano et al, 2000;Takano and Yamaguchi, 2007) using the energy gap by spin-polarized DFT calculations between the highest spin (HS) and lowest spin (LS) states,…”

Section: Magnetic Coupling Constant (J Ab )mentioning

confidence: 99%

“…However, spin-polarized DFT solutions in the LS states usually exhibit the broken symmetry problem (Isobe et al, www.intechopen.com 2002; Mitani et al, 2000a;Onishi et al, 2001;Salem, 1982;Takano et al, 2008;Takano et al, 2002a;Takano et al, 2001;Takano et al, 2000;Takano and Yamaguchi, 2007). Spin projection of the broken symmetry solutions should be carried out to eliminate the spin contaminations.…”

Section: Magnetic Coupling Constant (J Ab )mentioning

confidence: 99%

“…In order to obtain molecular orbital-theoretical explanation of the magnetic interactions, the natural orbitals of the spin-polarized DFT solutions were determined by diagonalizing their first-order density matrices (Onishi et al, 2001;Salem, 1982;Takano et al, 2008;Takano et al, 2002a;Takano et al, 2001;Takano et al, 2000;Takano and Yamaguchi, 2007) as…”

Section: Natural Orbitalsmentioning

confidence: 99%

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