Magnetic interactions in calcium and sodium ladder vanadates

Graaf, Coen de; Hozoi, Liviu; Broer, Ria

doi:10.1063/1.1630956

Cited by 26 publications

(33 citation statements)

References 63 publications

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“…Many calculations have shown the performance of DDCI estimates of the magnetic coupling. [20][21][22][23][24][25][26][27][28][29][30][31][32] The results reported in Table I show that the J values obtained at CAS+ S and DDCI2 levels are far from experimental ones, which suggest that an important part of the effects is missed. It is therefore concluded that 2h-1p and 1h-2p configurations bring from 30% to 50% of magnetic coupling.…”

Section: ͑8͒mentioning

confidence: 82%

“…So far, the DDCI approach has been extensively employed in the evaluation of J in molecular and solid state magnetic materials with a remarkable good agreement with experiment. [20][21][22][23][24][25][26][27][28][29][30][31][32] Some years ago we took benefit of this methodology to analyze in depth the physical contributions to the magnetic coupling on a series of binuclear Cu ͑II͒ complexes. 33 The use of the DDCI strategy allows not only to obtain quite accurate J values but also to analyze the various physical effects by generating CI spaces of increasing lengths that include different types of determinants.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of the magnetic coupling in binuclear systems. III. The role of the ligand to metal charge transfer excitations revisited

Calzado

Angeli

Taratiel

et al. 2009

The Journal of Chemical Physics

121

179

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In magnetic coordination compounds and solids the magnetic orbitals are essentially located on metallic centers but present some delocalization tails on adjacent ligands. Mean field variational calculations optimize this mixing and validate a single band modelization of the intersite magnetic exchange. In this approach, due to the Brillouin's theorem, the ligand to metal charge transfer ͑LMCT͒ excitations play a minor role. On the other hand the extensive configuration interaction calculations show that the determinants obtained by a single excitation on the top of the LMCT configurations bring an important antiferromagnetic contribution to the magnetic coupling. Perturbative and truncated variational calculations show that contrary to the interpretation given in a previous article ͓C. J. Calzado et al., J. Chem. Phys. 116, 2728 ͑2002͔͒ the contribution of these determinants to the magnetic coupling constant is not a second-order one. An analytic development enables one to establish that they contribute at higher order as a correlation induced increase in the LMCT components of the wave function, i.e., of the mixing between the ligand and the magnetic orbitals. This larger delocalization of the magnetic orbitals results in an increase in both the ferroand antiferromagnetic contributions to the coupling constant.

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Section: ͑8͒mentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Analysis of the magnetic coupling in binuclear systems. III. The role of the ligand to metal charge transfer excitations revisited

Calzado

Angeli

Taratiel

et al. 2009

The Journal of Chemical Physics

121

179

View full text Add to dashboard Cite

show abstract

“…This procedure makes use of the effective Hamiltonian theory, and it has been previously used in the study of magnetic systems, as well as the evaluation of hopping integrals in mixed-valence systems. [29][30][31][32][33][34][35][36][37][38][39][40][41] A detailed description of the method can be found in Ref. 41, and a summary enlightening the most striking points will be provided here.…”

Section: ͑4͒mentioning

confidence: 99%

“…This strategy has been extensively used in the recent past, especially in the evaluation of magnetic coupling constants as well as the determination of hopping integrals in numerous systems. [29][30][31][32][33][34][35][36][37][38][39][40][41]46,48,49,61,62 The whole procedure can be summarized as follows. ͑1͒ A fragment of the bulk structure of TiO 2 has been chosen, containing two neighbor Ti centers, and the ten oxygen atoms around them, as shown in Fig.…”

Section: Approximation To the Exact N-electron Wave Functionsmentioning

confidence: 99%

Effect of on-site Coulomb repulsion termUon the band-gap states of the reduced rutile (110)TiO2surface

2008

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We present a study concerning the effect of the on site d-d Coulomb interaction energy U on the band-gap states of nonstoichiometric rutile ͑110͒ TiO 2 surface. As well known, the excess electrons resulting from the formation of oxygen vacancies localize on the Ti 3d orbitals forming band-gap states. Local density approximation ͑LDA͒ does not give a correct description of these band-gap states, either with or without gradient corrections. The failure of LDA is often attributed to an inadequate treatment of electron correlation in systems with localized orbitals and is commonly corrected with an empirical local Coulomb repulsion term, i.e., the LDA+ U method. This study provides a completely general strategy to estimate the U value in this kind of systems, illustrated here for reduced ͑110͒ TiO 2 surface, well characterized from experiments. From ab initio embedded cluster configuration interaction calculations, combined with the effective Hamiltonian theory, a value of U of 5.5± 0.5 eV is obtained, in good agreement with those reported for this system from x-ray photoemission spectroscopy experiments ͑U = 4.5± 0.5 eV͒. It is observed that when the ab initio estimate of U is injected into the periodic LDA+ U calculations, a correct description of the gap states is obtained from the periodic LDA+ U calculations. Additionally, the results indicate that the position of these states on the band gap strongly depends on the level at which lattice relaxation is taken into account, with significant differences between the density of states curves at the LDA+ U level obtained using the optimal generalized gradient approximation or LDA+ U geometries. These results suggest that this combined strategy could be a useful tool for those systems where electron correlation plays a key role, and no experimental data are available for the on-site Coulomb repulsion.

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“…Furthermore, there exists by now substantial evidence in the literature that the electronic structure parameters considered here do not critically depend on the value of the charges to calculate the Madelung potential. [22][23][24] This observation only holds for ionic transition metal compounds. In case of materials with covalent bonds such as CuGeO 3 , the embedding procedure with formal charges does not lead to meaningful results and alternative embedding schemes should be applied.…”

Section: Computational Informationmentioning

confidence: 99%

Electronic structure ofCaCu2O3: Spin ladder versus one-dimensional spin chain

et al. 2005

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Quantum chemical calculations on embedded cluster models have been performed to extract accurate estimates of the magnetic coupling J and hopping parameters t of CaCu 2 O 3 . It is shown that this copper oxide compound is best described as a quasi-one-dimensional spin chain with weak interchain interactions within and between the Cu 2 O 3 planes. This magnetic structure is not reflected in the hopping parameters, since we find a large interplane hopping. Hence, the use of the simple second-order expression that relates J, t, and the on-site repulsion U ͑J =−4t 2 / U͒ is not justified in all cases.

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Magnetic interactions in calcium and sodium ladder vanadates

Cited by 26 publications

References 63 publications

Analysis of the magnetic coupling in binuclear systems. III. The role of the ligand to metal charge transfer excitations revisited

Analysis of the magnetic coupling in binuclear systems. III. The role of the ligand to metal charge transfer excitations revisited

Effect of on-site Coulomb repulsion termUon the band-gap states of the reduced rutile (110)TiO2surface

Electronic structure ofCaCu2O3: Spin ladder versus one-dimensional spin chain

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