Madelung fields from optimized point charges for <i>ab initio</i> cluster model calculations on ionic systems

Sousa, Carmen; Casanovas, Jordi; Rubió, J.; Illas, Francesc

doi:10.1002/jcc.540140608

Cited by 78 publications

(55 citation statements)

References 23 publications

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“…The final cluster models thus designed are Ni 2 O 11 and Ni 2 O 10 depending on whether the Ni-O-Ni magnetic path corresponds to an angle of 180°͑single bridge͒ or 90°͑double bridge͒. Total ion potentials ͑TIPs͒ 81 and an array of point charges 82,83 to account for the short-range and Madelung potential effects, respectively, surround both clusters.…”

Section: B Cluster Model Approachmentioning

confidence: 99%

Effect of Fock exchange on the electronic structure and magnetic coupling in NiO

2002

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The effect of Fock exchange on the periodic description of the geometrical structure, elastic constants, and electronic and magnetic properties of NiO is analyzed. Hybrid density functionals which combine a portion of ''exact'' Fock exchange with conventional local density approximation ͑LDA͒ or generalized gradient approximation ͑GGA͒ functionals remedy a number of serious inconsistencies with the traditional LDA or GGA descriptions of this prototypical ''Mott'' insulator. For example, the hybrid B3LYP functional ͑which mixes ϳ20% Fock exchange with GGA functionals͒ introduces a significant insulating gap and yields antiferromagnetic Heisenberg coupling constants between Ni sites (J 2 ) in semiquantitative agreement with experiment. Closer inspection shows that while the B3LYP orbital band gap is in excellent agreement with experiment, the magnitude of the antiferromagnetic coupling is overestimated by slightly more than 50%. This has led us to examine a simplified model which combines Fock exchange with the LDA exchange and correlation functionals. This combination allows us to study the magnitude and nature of the band gap, the magnitude of the unpaired spin densities in the different magnetic phases, and the two most important magnetic coupling constants as a function of the fraction of Fock exchange included. It is concluded that ϳ35% Fock exchange gives a reasonably balanced description of all properties, including structural parameters, magnetic form factors, the antiferromagnetic Ni-Ni exchange constant, and the character and magnitude of the band gap.

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Section: B Cluster Model Approachmentioning

confidence: 99%

Effect of Fock exchange on the electronic structure and magnetic coupling in NiO

2002

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“…15 The nickel oxygen distance ͑3.9344 bohr͒ was taken from experiment. 16 In both models the bridging oxygen is surrounded by four pseudopotentials as an improvement of the point charge approximation.…”

Section: A Materials Modelmentioning

confidence: 99%

On the magnetic coupling in NiO

Graaf

Illas

Broer

et al. 1997

The Journal of Chemical Physics

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The results are reported of ab initio calculations on the magnetic ordering in NiO, a prototype of the antiferromagnetic insulator. By analyzing wave functions for different cluster models, information is obtained about the physical effects determining the sign and the magnitude of the magnetic coupling parameter J. The role of the edge oxygens, surrounding the essential unit ͑Ni 2 O͒, is found to be quantitatively important but purely environmental in contrast to the role of the bridging oxygen. Furthermore, the importance of electron correlation and the usefulness of pseudopotentials in the calculations is investigated. The final result for J compares reasonably with experiment ͑about 50%͒, and possible sources for the remaining discrepancies are discussed.

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“…Since calculating the EFG was the main goal, it was deemed essential to add and scale these charges to correctly reproduce the Madelung potential at the site of the atom of interest. 42 Calculations were carried out on a cluster, but were not parallelized. Each node is a DELL GX270 workstation with 2 GB of RAM, and calculation times varied from 24 to 48 h.…”

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High Field ³³S Solid State NMR and First-Principles Calculations in Potassium Sulfates

et al. 2009

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Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/view/object/?id=0b178185-620e-4262-8966-6e518a9bdcdf http://nparc.cisti-icist.nrc-cnrc.gc.ca/fra/voir/objet/?id=0b178185-620e-4262-8966-6e518a9bdcdf High Field S Solid State NMR and First-Principles Calculations in Potassium SulfatesIgor Moudrakovski,* Stephen Lang, Serguei Patchkovskii, and John Ripmeester Steacie Institute for Molecular Sciences, National Research Council, 100 Sussex DriVe, Ottawa, K1A 0R6, Ontario, Canada ReceiVed: August 25, 2009; ReVised Manuscript ReceiVed: October 16, 2009 A set of potassium sulfates presenting a variety of sulfur environments (K 2 SO 4 , KHSO 4 ,K 2 S 2 O 7 , and K 2 S 2 O 8 ) has been studied by 33 S solid state NMR at 21 T. Low natural abundance (0.75%) and small gyromagnetic ratio of 33 S presented a serious challenge even at such a high magnetic field. Nevertheless, using the QCPMG technique we were able to obtain good signals from the sites with C Q values approaching 16 MHz. Assignment of the sites and the relative orientations of the EFG tensors were assisted by quantum mechanical calculations using the Gaussian 98 and CASTEP packages. The Gaussian 98 calculations were performed using the density functional method and gauge independent atomic orbitals on molecular clusters of about 100-120 atoms. The CASTEP calculations utilized periodic boundary conditions and a gauge-including projector augmentedwave pseudopotential approach. Although only semiquantitative agreement is observed between the experimental and calculated parameters, the calculations are a very useful aid in the interpretation of experimental data.

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Madelung fields from optimized point charges for ab initio cluster model calculations on ionic systems

Cited by 78 publications

References 23 publications

Effect of Fock exchange on the electronic structure and magnetic coupling in NiO

Effect of Fock exchange on the electronic structure and magnetic coupling in NiO

On the magnetic coupling in NiO

High Field ³³S Solid State NMR and First-Principles Calculations in Potassium Sulfates

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Madelung fields from optimized point charges for ab initio cluster model calculations on ionic systems

Cited by 78 publications

References 23 publications

Effect of Fock exchange on the electronic structure and magnetic coupling in NiO

Effect of Fock exchange on the electronic structure and magnetic coupling in NiO

On the magnetic coupling in NiO

High Field 33S Solid State NMR and First-Principles Calculations in Potassium Sulfates

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High Field ³³S Solid State NMR and First-Principles Calculations in Potassium Sulfates