Gradient-corrected density-functional studies of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">CaCuO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Dj, Singh; Pickett, W. E.

doi:10.1103/physrevb.44.7715

Cited by 35 publications

(12 citation statements)

References 27 publications

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“…[5][6][7][8][9][10][11][12][13][14][15] In contrast to the local spin density approximation ͑LSDA͒ applied to cuprates, 16 hybrid functionals correctly predict parent compounds of doped cuprates to be antiferromagnetic insulators. [8][9][10][11] The B3LYP hybrid functional 17,18 predicts the band gap of a range of oxides quite accurately.…”

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confidence: 99%

Electronic structure and lattice vibrations ofCa2CuO2Cl2: A hybrid density functional study

Patterson

2008

Phys. Rev. B

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The electronic structure and phonon modes of Ca 2 CuO 2 Cl 2 have been calculated using hybrid density functional theory ͑HDFT͒ methods. The material is correctly predicted to be an antiferromagnetic insulator with a band gap of around 2 eV. Lattice parameters and atomic positions are in good agreement with experiment with a maximum error in lattice constant less than 2%. Phonon modes were calculated using HDFT Hamiltonians containing Hartree-Fock ͑HF͒ exchange with weights of 0.2, 0.3, or 0.4. Phonon mode frequencies typically shift upward by 4% on increasing the HF exchange weight by 0.1. Computed Cu-O stretching modes of E u symmetry at 615 and 334 cm −1 are in good agreement with recently reported IR absorption frequencies at 620 and 350 cm −1 .

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confidence: 99%

Electronic structure and lattice vibrations ofCa2CuO2Cl2: A hybrid density functional study

Patterson

2008

Phys. Rev. B

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“…The reported values of U for the 3d orbitals of divalent Cu ions range between 4 and 8 eV, which were obtained using the constrained-density-functional method in a first-principles manner or by empirically fitting the band gaps. [32][33][34][35][36] In this study, we used three different values of U, namely, 7, 8, and 9 eV, and set J at 1 eV, which is a common value for 3d transition-metal compounds. This corresponds to UЈ =6, 7, and 8 eV.…”

Section: Computational Proceduresmentioning

confidence: 99%

First-principles study of defect-induced potentials inCa2CuO2Cl2

et al. 2009

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The local atomic and electronic structures of the Na and K impurities and the vacancy at the Ca site ͑Na Ca , K Ca , and V Ca ͒, and their induced electrostatic potentials in Ca 2 CuO 2 Cl 2 have been investigated by using the GGA+ U approach. It is found that Na Ca and K Ca are markedly relaxed toward the Cl plane from the original Ca site. When V Ca exists, its neighboring Ca approaches the vacancy site, and Cl and O are relaxed outwardly. From the analyses of the local electrostatic potentials at the Cu and O sites, we found that the Na Ca -induced potential is almost the same as the K Ca -induced potential, and the V Ca -induced potential is about twice as large. The defect-induced potentials are modeled by point charges under a dielectric medium. The atomic relaxation is found to increase the effective dielectric constants approximately threefold, indicating the importance of its contribution to the screening of the potential. The stabilization energies of small polarons obtained by the total energy differences are close to the potential energies. These results suggest that the interaction between the polaron and defects is well described by a positive charge of the polaron under the defect-induced electrostatic potential.

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“…The greatest limitation of conventional density functional methods, when applied to insulating transition metal oxides, is their tendency to predict them to be metallic. 14,15 This limitation is removed either by using the LDA+ U approach, in which a Hubbard U term is added to the density functional Hamiltonian, or by adding a Hartree-Fock exchange term to the Hamiltonian, as is done in the hybrid density functional methods used in this work. As noted above, the B3LYP functional used in this work correctly predicts the undoped compound, CCOC, to be an antiferromagnetic insulator.…”

Section: A Limitations Of Mean Field Approachesmentioning

confidence: 99%

“…11 These observations are in sharp contrast to density functional theory studies which omit a Hubbard U term, in which case the antiferromagnetic, insulating parent compound is usually predicted to be metallic. 14,15 An extensive model Hamiltonian study of striped phases of cuprates found linear chains of holes in a half-filled stripe state 16 and the formation of charged lines of holes on oxygen ions in CuO 2 planes was predicted using Hubbard models. [17][18][19] A hybrid density functional approach, 20,21 which includes Hartree-Fock exchange with a weighting factor, is used to study hole states in Ca 2−x Na x CuO 2 Cl 2 ͑Na-CCOC͒, with x = 0.0625 and 0.125 in this work; inclusion of Hartree-Fock exchange in the Hamiltonian leads to a polaronic description of hole states in cuprates and other oxides 8,9,22 and correctly predicts an antiferromagnetic insulating state for the parent compound of the doped cuprates studied here.…”

Section: Introductionmentioning

confidence: 99%

Small polarons and magnetic antiphase boundaries inCa2−xNaxCuO2Cl
Patterson
¹

2008
Phys. Rev. B
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We report hybrid density functional theory calculations on hole doped Ca 2−x Na x CuO 2 Cl 2 performed in 4 ϫ 4, 4 ͱ 2 ϫ 4 ͱ 2, and 8 ϫ 2 supercells with hole concentrations x = 0.0625 and x = 0.125. Holes at the lower concentration form small polarons, in which the hole is mainly localized on four oxygen ions surrounding one copper ion. The polaron is a spin one-half ferromagnetic polaron ͑Cu 5 O 4 ͒, in which the moment on the central copper ion is parallel to those on the four neighboring copper ions and the moment on the oxygen ions is opposed to that on the copper ions. This is therefore an Emery-Reiter spin polaron rather than a Zhang-Rice singlet. At the higher hole concentration ͑x = 0.125͒, many cuprates form stripes. Hybrid density functional theory calculations on linear chains of spin polarons separated by 4a 0 show a group of bands localized mainly on the stripe. Spins on neighboring copper ions in the stripe are parallel and so the stripe forms a magnetic antiphase boundary between antiferromagnetically ordered blocks of copper spins. Stripes of this kind, which run in one direction only, may explain recent scanning tunneling microscopy data from Ca 2−x Na x CuO 2 Cl 2 by Kohsaka et al. ͓Science 315, 1380 ͑2007͔͒. We also consider an ordered spin polaron phase where magnetic antiphase boundaries intersect at right angles. In this case, sets of four copper ions in squares at stripe intersections have parallel spins. This phase may be the 4 ϫ 4 checkerboard pattern reported by Hanaguri et al. ͓Nature ͑London͒ 430, 1001 ͑2004͔͒.

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Gradient-corrected density-functional studies ofCaCuO2

Cited by 35 publications

References 27 publications

Electronic structure and lattice vibrations ofCa2CuO2Cl2: A hybrid density functional study

Electronic structure and lattice vibrations ofCa2CuO2Cl2: A hybrid density functional study

First-principles study of defect-induced potentials inCa2CuO2Cl2

Small polarons and magnetic antiphase boundaries inCa2−xNaxCuO2Cl
Patterson
¹

2008
Phys. Rev. B
18
0
9
0
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Gradient-corrected density-functional studies ofCaCuO2

Cited by 35 publications

References 27 publications

Electronic structure and lattice vibrations ofCa2CuO2Cl2: A hybrid density functional study

Electronic structure and lattice vibrations ofCa2CuO2Cl2: A hybrid density functional study

First-principles study of defect-induced potentials inCa2CuO2Cl2

Small polarons and magnetic antiphase boundaries inCa2−xNaxCuO2ClPatterson1 2008Phys. Rev. B18090View full textAdd to dashboardCite

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Small polarons and magnetic antiphase boundaries inCa2−xNaxCuO2Cl
Patterson
¹

2008
Phys. Rev. B
18
0
9
0
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