<i>Ab initio</i>valence-bond cluster model for ionic solids: Alkaline-earth oxides

Lorda, A.; Illas, Francesc; Rubió, J.; Torrance, J. B.

doi:10.1103/physrevb.47.6207

Cited by 20 publications

(8 citation statements)

References 29 publications

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“…The energy gaps between the conduction and valence bands of the Mg 10 O 8 , Ca 10 O 8 and Sr 10 O 8 clusters without geometric relaxation were determined to be 5.6, 4.6, and 4.2 eV, respectively, which are consistent with the observed bulk energy-band gaps ͑7.7-7.8, 6.8-7.1, and 5.8-6.0 eV, respectively͒. 12 The discrepancy between the obtained band gaps and the observed bulk ones is generated by terminal effects of the clusters modeling defective corners, and not by any inaccuracy in the computational method. This is, in fact, confirmed by calculating a bulk-type Sr 14 O 14 cluster with 698 point charges.…”

Section: Cluster Models and Computational Methodssupporting

confidence: 79%

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Comparative study of oxygen double exchange betweenO2adsorbate and alkaline-earth oxides

et al. 1996

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Thermal desorption of doubly exchanged oxygen molecules at temperatures above 800 K is observed not from MgO but from CaO and SrO powders after 18 O 2 -gas exposure at room temperature. The exchange reaction was investigated using ab initio molecular-orbital calculations. The defective ͑111͒ surface clusters of CaO and SrO were found to prepare anion-charged reactive centers to accept the O 2 adsorbate. The adsorbate was incorporated into a key O 5 -charged intermediate which can provide an oxygen molecule composed of two lattice atoms for desorption. The nonreactive character of the MgO surface in the ground state is ascribed to the presence of oxygen ions bound strongly at the lattice points. ͓S0163-1829͑96͒04344-5͔

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Section: Cluster Models and Computational Methodssupporting

confidence: 79%

“…The large model is found to give a gap of 6.0 eV, which is satisfactorily in the experimental range of 5.8-6.0 eV. 12 Here single point defects on flat ͑001͒ surfaces are not taken into consideration. This is because their inactivity is well established.…”

Section: Cluster Models and Computational Methodsmentioning

confidence: 52%

Comparative study of oxygen double exchange betweenO2adsorbate and alkaline-earth oxides

et al. 1996

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“…There are several possible choices for the one-electron MO basis set. One can simply take orthogonal atomic orbitals (OAO) which correspond to the ab initio valence bond model recently reported [18], use MOs from a Hartree-Fock self-consistent field (SCF) calculation in the highest multiplet or those from a multiconfigurational self-consistent field (MCSCF) cal- culation in the lowest state. It is also possible to analyze the effects introduced when going from the purely ab initio ionic model to the SCF functions by using the constrained space orbital variation (CSOV) method [19,20].…”

Section: H\q)-e Q \Q)--j\q)mentioning

confidence: 99%

Towards anab initiodescription of magnetism in ionic solids

et al. 1993

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The physical contributions to the KNiF3 magnetic exchange coupling integral have been obtained from specially designed ab initio cluster model calculations. Three important mechanisms have been identified. These are the derealization of the magnetic orbitals into the anion "p" band, the variational contribution of the second-order interactions, and the many-body terms "hidden" in the two-body operator of the Heisenberg Hamiltonian.PACS numbers: 75.10.Jm, 71.10.+x Magnetic properties of ionic solids have experienced a renewed interest due to the discovery of high-7V superconductors [1,2]. A relationship between magnetism and superconductivity arises from the new superconductor mother compounds, such as La2CuC>4, which are antiferromagnetic insulators close to the Mott transition [3]. From the point of view of theory, two approaches have been used. The first one is based on local spin-density calculations [4] whereas the second one uses simplified model Hamiltonians [5][6][7]. While highly desirable, a fully ab initio description has not been reported yet. The reason for this lack is that, in spite of the high degree of accuracy that can be achieved by the modern quantum chemistry, the problem of magnetism in solids is very difficult since it involves very small energy differences.For molecular complexes, de Loth et al.[8] suggested a second-order nonempirical treatment based on the theory of effective Hamiltonians. A variational version of this procedure has been reported recently and generalized to different physical situations [9,10]. In principle, there is no reason why such theoretical approaches could not be applied to solids as well if a suitable model is used. This is the aim of the present work.In a series of papers Malrieu and co-workers have used a magnetic model to study alkali metals, conjugated hydrocarbons, and related systems [11][12][13][14]. In this model the exchange coupling integral C/) is extracted from accurate calculations in simple models. The idea behind this approach is very attractive because it implies that the magnetic behavior of extended systems can be obtained from nonempirical model Hamiltonians with parameters extracted from accurate quantum chemical calculations on small models, usually dimers.The aim of this work is to explore the magnetic structure of a simple ionic solid such as KNiF3 using a parameter-free approach (see also Refs. [15,16]). We will use different cluster models for KNiF 3 and different ab initio wave functions to show that there are three main factors governing magnetism in KNiF3. For the first time, we will quantify the importance of these contributions to the final coupling exchange constant. The KNiF3 cubic perovskite is known to be an excellent example of a simple nearest-neighbor exchange Heisenberg system. The spin Hamiltonian can be written simply as where (ij) means that the summation in (1) is over all nearest-neighbor pairs / and j Ni 2+ cations on KNiF3 structure. Moreover, the ground state of Ni 2+ in KNiF3 is 3 F so each cation can be simply se...

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“…See, for instance, the study on NiO and CuO by Parmigiani et al? 4 The use of OPC, as suggested in the present work, is a simple and straight way to avoid this source of error.…”

Section: Selected Calculationsmentioning

confidence: 98%