Cluster Calculations of Hyperfine Interactions in Superconducting Copper Compounds

Meier, P. F.; Claxton, T. A.; Hüsser, P.; Pliberšek, S.; Stoll, E.

doi:10.1515/zna-2000-1-244

Cited by 2 publications

(1 citation statement)

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“…The on-site contact hyperfine field is negative (−1.78 a −3 B ) but there exists a positive field that is transferred from nearest neighbour copper ions (+0.71 a −3 B ). A detailed analysis of these calculated spin transfers has been given [20,21]. Here, we first note that the theoretical results are in very good agreement with the values derived from the NMR data [22,23].…”

Section: Further Observationssupporting

confidence: 75%

On the distribution of intrinsic holes in cuprates

Stoll

Meier

Claxton

2003

J. Phys.: Condens. Matter

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First-principles density functional calculations on the La2CuO4 crystal, simulated by using the Cu5O26/Cu8La34 cluster, have been analysed to reveal that the Cu 4s orbital is occupied by about 0.5 electrons. Since this may have important consequences on the method of calculation of the intrinsic hole distribution in cuprates, a study of the frontier orbitals has been made. It is concluded that the Cu 4s occupancy is a direct result of a charge transfer from the oxygen anions but does not involve the hole. It is a clear illustration that the hole distribution cannot always be estimated from the charge density distribution alone. 60% of the hole remains on the copper while the rest is spread evenly about the planar oxygen atoms.

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Section: Further Observationssupporting

confidence: 75%

On the distribution of intrinsic holes in cuprates

Stoll

Meier

Claxton

2003

J. Phys.: Condens. Matter

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Electric field gradients from first-principles and point-ion calculations

2002

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Point-ion models have been extensively used to determine "hole numbers" at copper and oxygen sites in high-temperature superconducting cuprate compounds from measured nuclear quadrupole frequencies. The present study assesses the reliability of point-ion models to predict electric field gradients accurately and also the implicit assumption that the values can be calculated from the "holes" and not the total electronic structure. First-principles cluster calculations using basis sets centred on the nuclei have enabled the determination of the charge and spin density distribution in the CuO2-plane. The contributions to the electric field gradients and the magnetic hyperfine couplings are analysed in detail. In particular they are partitioned into regions in an attempt to find a correlation with the most commonly used point-ion model, the Sternheimer equation which depends on the two parameters R and γ. Our most optimistic objective was to find expressions for these parameters, which would improve our understanding of them, but although estimates of the R parameter were encouraging the method used to obtain the γ parameter indicate that the two parameters may not be independent. The problem seems to stem from the covalently bonded nature of the CuO2-planes in these structures which severely questions using the Sternheimer equation for such crystals, since its derivation is heavily reliant on the application of perturbation theory to predominantly ionic structures. Furthermore it is shown that the complementary contributions of electrons and holes in an isolated ion cannot be applied to estimates of electric field gradients at copper and oxygen nuclei in cuprates.

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Cluster Calculations of Hyperfine Interactions in Superconducting Copper Compounds

Cited by 2 publications

References 1 publication

On the distribution of intrinsic holes in cuprates

On the distribution of intrinsic holes in cuprates

Electric field gradients from first-principles and point-ion calculations

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