| 1. |
- Bengone, Oliver, et al.
(författare)
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Electronic structure and transport properties of CrAs/GaAs/CrAs trilayers from first principles theory
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:3
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical study of the transport properties of a CrAs/GaAs/CrAs trilayer. The theory was based on a first principles method for calculating the electronic structure, in combination with a Kubo-Landauer approach for calculating the transport properties in a current perpendicular to the plane geometry. We have also investigated the electronic structure and the magnetic properties of this trilayer, with special focus on electronic and magnetic properties at the CrAs/GaAs interface. Finally, we have studied the effects of chemical disorder on the transport properties, in particular the influence of As antisites at both the Cr and Ga sites.
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| 2. |
- Bengone, Oliver, et al.
(författare)
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Origin of the negative giant magnetoresistance effect in Co1-xCrx/Cu/Co (111) trilayers
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:9, s. 092406-
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical study on Co1-xCrx/Cu/Co (111) trilayers, where a transition from positive to negative giant magnetoresistance effect has been observed experimentally, with increasing thickness of the alloyed layer. The theory, based on a recently implemented conductance calculation, reproduces quantitatively this observation, and the effect is found to be caused by alloying effects, due to a virtual bound Cr d state in the majority spin channel of the Co-Cr layer.
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| 3. |
- Fransson, Jonas, et al.
(författare)
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A physical compact model for electron transport across single molecules
- 2006
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Ingår i: IEEE transactions on nanotechnology. - 1536-125X .- 1941-0085. ; 5:6, s. 745-749
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Tidskriftsartikel (refereegranskat)abstract
- Prediction of current flow across single molecules requires ab initio electronic structure calculations along with their associated high computational demand, and a means for incorporating open system boundary conditions to describe the voltage sources driving the current. To date, first principle predictions of electron transport across single molecules have not fully achieved a predictive capability. The situation for molecular electronics may be compared to conventional technology computer-aided design (TCAD), whereby various approximations to the Boltzmann transport equation are solved to predict electronic device behavior, but in practice are too time consuming for most circuit design applications. To simplify device models for circuit design, analytical but physically motivated models are introduced to capture the behavior of active and passive devices; however, similar models do not vet exist for molecular electronics. We follow a similar approach by evaluating an analytical model achieved by combining a mesoscopic transport model with parameterizations taken from quantum chemical calculations of the electronic structure of single molecule bonded between two metal contacts. Using the model to describe electron transport across benzene- 1,4-dithiol and by comparing to experiment, we are able to extract the coupling strength of the molecule attached to two infinite metal electrodes. The resulting procedure allows for accurate and computationally efficient modeling of the static (dc) characteristics of a single molecule, with the added capability of being able to study the physical model parameter variations across a range of experiments. Such simple physical models are also an important step towards developing a design methodology for molecular electronics.
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| 4. |
- Le Bacq, O, et al.
(författare)
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Impact on electronic correlations on the structural stability, magnetism, and voltage of LiCoPO4 battery
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:24, s. 245107-
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of the structural stability of the lithium-orthophosphate oxide LiCoPO4 using density-functional theory within the local-density (LDA), generalized gradient and LDA+U approximation. We show that both enhanced localization and anisotropic effects provided within the LDA+U approximation are essential to reproduce the experimentally observed magnetic structure, lattice parameters, and stability of the lithiated and nonlithiated compound. Within this approximation, the intercalation voltage of 4.6 eV as well as the insulator character of the lithiated and nonlithiated compounds are recovered. Moreover, we found that the LDA+U approximation induces a strong transfer of charge from the t(2g)-like to the e(g)-like orbitals of Co as well as a significant shift of the LiPO4 band. Both effects are competing with each other and determine most of the peculiar properties of the LiCoPO4 and CoPO4 compounds.
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| 5. |
- Muscarella, Robert, et al.
(författare)
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The global abundance of tree palms
- 2020
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Ingår i: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 29:9, s. 1495-1514
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Tidskriftsartikel (refereegranskat)abstract
- AimPalms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change.LocationTropical and subtropical moist forests.Time periodCurrent.Major taxa studiedPalms (Arecaceae).MethodsWe assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., ≥10 cm diameter at breast height) abundance relative to co‐occurring non‐palm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure.ResultsOn average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of long‐term climate stability. Life‐form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non‐tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above‐ground biomass, but the magnitude and direction of the effect require additional work.ConclusionsTree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be particularly crucial in Neotropical forests.
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| 6. |
- Wessely, Ola, et al.
(författare)
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Initial and final state effects in the x-ray absorption process of La1-xSrxMnO3
- 2003
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Ingår i: Physical Review B : Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:23, s. 235109-1
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Tidskriftsartikel (refereegranskat)abstract
- We have probed the electronic structure of La1-xSrxMnO3 using x-ray absorption spectroscopy, and compared our results to theory. It is shown that the O projected spectrum reveals a signal that is consistent only with hybridized and delocalized Mn d-states whereas the Mn projected spectrum reveals a signal that can only be reproduced by atomic like theory allowing for multiplet formation between the core hole and the valence electrons of the final state. Our results indicate that the ground state electronic structure has delocalized Mn d-states. This is discussed to be caused by a dynamical screening of the core hole created in the absorption process.
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| 7. |
- Wessley, O, et al.
(författare)
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Final state effects in the X-ray absorption spectra of La0.7Sr0.3MnO3
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 272-276:3, s. 1780-1781
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Tidskriftsartikel (refereegranskat)abstract
- We present a comparison of theoretical calculations of the electronic structure of La0.7Sr0.3MnO3 with measurements of the unoccupied local density of states for Mn obtained from X-ray absorption spectroscopy (XAS). We compare two different theoretical calculations of the Mn XAS spectra, one based on the local spin density approximation (LSDA) and the other one based on an atomic Hartree–Fock calculation for the Mn ions. In the atomic calculation the solid state effects are introduced through a cubic crystal field where the crystal field strength is obtained from the LSDA calculation. It is found that the atomic calculations agree better with experimental data.
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