| 1. |
- Azuri, Ido, et al.
(författare)
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Fe-porphyrin on Co(001) and Cu(001) : A Comparative Dispersion-augmented Density Functional Theory Study
- 2020
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Ingår i: Israel Journal of Chemistry. - : Wiley. - 0021-2148 .- 1869-5868. ; 60:8-9, s. 870-875
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Tidskriftsartikel (refereegranskat)abstract
- We present a comparative density functional theory (DFT) investigation of the interaction of the iron porphyrin (FeP) molecule with the metallic Co(001) and Cu(001) surfaces, with the aim of elucidating the effect of different choices for the treatment of dispersion. We compare a GGA+U approach, several flavors of dispersion-augmented terms, and two variants of the vdW-DF approach, which treats long-range correlation explicitly. For the Co surface, we find that all approaches predict chemisorption and a high-spin state, although vdW-DF functionals generally predict weaker bonds and weaker chemisorption. For the Cu surface, we find that the functionals augmented by pair-wise dispersion once again predict chemisorption and a preferred HS state, but the vdW-DF functionals predict physisorption and a LS state. These results demonstrate the importance of careful assessment of the level of theory at which dispersion is treated, as this may have significant quantitative and even qualitative effects on the predictions made. The results also call for additional experimental data for these systems.
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| 2. |
- Makmal, Adi, et al.
(författare)
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Examining the role of pseudopotentials in exact-exchange-based Kohn-Sham gaps
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 80:16, s. 161204-
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Tidskriftsartikel (refereegranskat)abstract
- We present exact-exchange calculations of the Kohn-Sham gap, as well as the fundamental gap resulting from it, using highly accurate grid-based all-electron and pseudopotential approaches for prototypical diatomic molecules. Results obtained with pseudopotentials that have been constructed in a manner consistent with the exact-exchange functional agree with the all electron results for the cases studied. This confirms the reliability of the pseudopotential approximation for orbital-dependent functionals such as exact exchange.
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| 3. |
- Mondal, Amit Kumar, et al.
(författare)
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Long-Range Spin-Selective Transport in Chiral Metal-Organic Crystals with Temperature-Activated Magnetization
- 2020
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Ingår i: ACS Nano. - : AMER CHEMICAL SOC. - 1936-0851 .- 1936-086X. ; 14:12, s. 16624-16633
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Tidskriftsartikel (refereegranskat)abstract
- Room-temperature, long-range (300 nm), chirality-induced spin-selective electron conduction is found in chiral metal-organic Cu(II) phenylalanine crystals, using magnetic conductive-probe atomic force microscopy. These crystals are found to be also weakly ferromagnetic and ferroelectric. Notably, the observed ferromagnetism is thermally activated, so that the crystals are antiferromagnetic at low temperatures and become ferromagnetic above similar to 50 K. Electron paramagnetic resonance measurements and density functional theory calculations suggest that these unusual magnetic properties result from indirect exchange interaction of the Cu(II) ions through the chiral lattice.
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| 4. |
- Rangel, Tonatiuh, et al.
(författare)
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Structural and excited-state properties of oligoacene crystals from first principles
- 2016
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 93
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Tidskriftsartikel (refereegranskat)abstract
- Molecular crystals are a prototypical class of van der Waals (vdW) bound organic materials with excited state properties relevant for optoelectronic applications. Predicting the structure and excited state properties of molecular crystals presents a challenge for electronic structure theory, as standard approximations to density functional theory (DFT) does not cover the long ranged vdW dispersion interactions and do not yield excited state properties. In this work we use a a combination of DFT including vdW forces -- using both nonlocal functionals and pair-wise correction methods -- together with many-body perturbation theory (MBPT) to study the geometry and excited states, respectively, of the entire set of oligoacene crystals, from benzene to hexazene. We find that vdW methods can predict lattice constants within 1 percent of the experimental measurements, on par with the previously reported accuracy of the pair-wise approximations for the same systems. We further find that the excitations energies are sensitive to the geometry, but if optimized geometries are used MBPT can yield excited state properties within a few tenths of an eV from experiments. We elucidate trends in MBPT-charge and neutral excitation energies across the acene series and discuss the role of common approximations used in MBPT.
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| 5. |
- Viswanatha, Ranjani, et al.
(författare)
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Magnetic Properties of Fe/Cu Codoped ZnO Nanocrystals
- 2012
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 3:15, s. 2009-2014
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Tidskriftsartikel (refereegranskat)abstract
- Free-standing ZnO nanocrystals simultaneously doped with Fe and Cu with varying Fe/Cu compositions have been synthesized using colloidal methods with a mean size of similar to 7.7 nm. Interestingly, while the Cu-doped ZnO nanocrystal remains diamagnetic and Fe-doped samples show antiferromagnetic interactions between Fe sites without any magnetic ordering down to the lowest temperature investigated, samples doped simultaneously with Fe and Cu show a qualitative departure in exhibiting ferromagnetic interactions, with suggestions of ferromagnetic order at low temperature. XAS measurements establish the presence of Fe2+ and Fe3+ ions, with the concentration of the trivalent species increasing in the presence of Cu doping, providing direct evidence of the Fe2+ + Cu2+ sic Fe3+ + Cu+ redox couple being correlated with the ferromagnetic property. Using DFT, the unexpected ferromagnetic nature of these systems is explained in terms of a double exchange between Fe atoms, mediated by the Cu atom, in agreement with experimental observations.
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