| 1. |
- Amft, Martin, et al.
(författare)
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Adsorption of Cu, Ag, and Au atoms on graphene including van der Waals interactions
- 2011
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 23:39
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Tidskriftsartikel (refereegranskat)abstract
- We performed a systematic density functional (DF) study of the adsorption of copper, silver, and gold adatoms on pristine graphene, especially accounting for van der Waals (vdW) interactions by the vdW-DF and PBE + D2 methods. In particular, we analyze the preferred adsorption site (among top, bridge, and hollow positions) together with the corresponding distortion of the graphene sheet and identify diffusion paths. Both vdW schemes show that the coinage metal atoms do bind to the graphene sheet and that in some cases the buckling of the graphene layer can be significant. Only the results for silver are qualitatively at variance with those obtained with the generalized gradient approximation, which gives no binding in this case. However in all three cases, we observe some quantitative differences between the vdW-DF and PBE + D2 methods. For instance the adsorption energies calculated with the PBE + D2 method are systematically higher than the ones obtained with vdW-DF. Moreover, the equilibrium distances computed with PBE + D2 are shorter than those calculated with the vdW-DF method.
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| 2. |
- Araujo, Carlos Moyses, et al.
(författare)
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Electronic and optical properties of MgH2: a first-principle GW investigation
- 2005
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 98:9, s. 096106-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of MgH2 is studied using the state of the art all-electron projector-augmented-wave GW approximation. Both the ground-state and the high-pressure transformations are considered in this investigation. We have found an indirect (direct) band-gap of 5.58 eV (6.52 eV) for α-MgH2, which has a good agreement with the experimental findings. For the γ- and β-phases, we have found indirect (direct) band-gap values of 5.24 eV (5.33 eV) and 3.90 eV (4.72 eV), respectively. The optical properties are investigated by means of the complex dielectric function, which is calculated within the framework of a full-potential linearized augmented plane wave method and corrected by scissor operators. All phases are found to be color neutral insulators.
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| 3. |
- Ben Romdhane, Ferdaous, et al.
(författare)
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Quasi-2D Cu2S Crystals on Graphene : In-situ Growth and ab-initio Calculations
- 2015
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Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 11:11, s. 1253-1257
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional crystals of beta-copper sulfide are synthesized in an in-situ electron microscopy experiment. Copper crystals are deposited on an amorphous carbon film containing sulfur. The carbon film graphitizes upon heating and electron irradiation and allows the reaction of Cu and S towards two-dimensional Cu2S crystals. These are energetically favourable and bonded via van der Waals interactions to the graphitic substrate.
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| 4. |
- Debbichi, Lamjed, et al.
(författare)
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Electronic structure of In3Se4 and In3Te4 monolayers from ab-initio calculations
- 2014
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Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 526:9-10, s. 402-407
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Tidskriftsartikel (refereegranskat)abstract
- First principles calculations have been used to calculate the interlayer binding energy, the phonons frequencies, and the electronic structure of the In3X4 layered systems, with X = Se or Te. Using density functional theory corrected to take into account van der Waals interactions, the binding energy was found to be approximate to 41-44meV for In3Se4 and approximate to 53-58meV for In3Te4. Moreover, the absence of imaginary frequencies in the phonons bandstructures demonstrates the dynamical stability of the isolated layers. These facts suggest that isolated layers of In3Se4 and In3Te4 could be obtained by means of exfoliation from the bulk.
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| 5. |
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| 6. |
- Eriksson, Olle, et al.
(författare)
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Many-body projector orbitals for electronic structure theory of strongly correlated electrons
- 2005
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Ingår i: INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY. - : Wiley. - 0020-7608 .- 1097-461X. ; 105:2, s. 160-
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Tidskriftsartikel (refereegranskat)abstract
- We describe a technique to evaluate projector functions to be used, e.g., in self-interaction corrected versions of the Kohn-Sham equation (or in the LSDA+U method). The projector functions reproduce by construction the expectation values of spin and orbital moments (or any other property one is interested in) for the atomic many-body state. We therefore refer to these projector functions as many-body projector orbitals (MBPO). We describe how, once these projector states have been calculated, one can use them in any electronic structure method for a solid or molecule, to calculate ground-state properties of materials with strongly correlated states.
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| 7. |
- Lebegue, Sebastien, et al.
(författare)
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Ab initio study of the electronic properties and Fermi surface of the uranium dipnictides
- 2006
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Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 73:4, s. 045119-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the uranium dipnictides UX2 (X=As, Sb, and Bi) is investigated by means of ab initio calculations based on density functional theory. The calculated Fermi surfaces are presented and compared to available experimental models obtained from de Haas-van Alphen experiments. In agreement with experiments they are found to have a significant two-dimensional character. Also, the change of the electronic properties through the series is discussed.
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| 8. |
- Lebegue, Sebastien, et al.
(författare)
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Electronic structure and spectroscopic properties of thulium monochalcogenides
- 2005
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Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 72:24, s. 245102-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the thulium monochalcogenides TmS, TmSe, and TmTe is studied with several theoretical approaches. The total energy is evaluated with the self-interaction corrected local-spin density approximation, whereby the Tm ions are described with either twelve or thirteen localized f electrons with the remaining electrons forming bands. The comparisons of these two scenarios reveal the valency shift of the Tm ion through the series. The spectral functions of TmX compounds are calculated including multiplet effects, and they are compared to experimental x-ray photoemission spectra. The basic tool is the Hubbard-I approximation in which the embedding of an isolated f(n) ion in a solid is performed by modifying the crystal Hamiltonian as obtained from the local-density approximation with the atomic self-energy of the ion. The parameters of the model are obtained from the self-consistent band structure calculation. The agreement with experiment is excellent, reproducing all significant multiplet structures.
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| 9. |
- Lebègue, Sébastien, et al.
(författare)
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Molecular dynamics simulation and chemical bonding analysis of MgB2C2
- 2006
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Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 37:3, s. 220-225
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Tidskriftsartikel (refereegranskat)abstract
- The possible superconducting material MgB2C2 is studied by means of the Projector Augmented Plane wave method. The experimental lattice parameters and internal coordinates are reproduced with accuracy by means of a molecular dynamics calculation. A chemical bonding analysis is performed and it is found that the charge transfer from the Mg atoms to the BC network is not complete, meaning that a significant part of covalent bonding is present in this bond. In addition, a crystal orbital overlap population calculation reveals the degree of covalent bonding between atoms. This analysis is of particular importance and helps improve our general understanding of the superconductivity in these type of materials.
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| 10. |
- Lebègue, Sebastien, et al.
(författare)
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Multiplet effects in the electronic structure of heavy rare-earth metals
- 2006
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Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 18, s. 6329-
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Tidskriftsartikel (refereegranskat)abstract
- The spectroscopic properties of elemental terbium, dysprosium, holmium, and erbium are investigated using first-principles calculations taking into account intra-atomic correlation effects. In order to describe the strongly localized f electrons together with the conduction bands, we have used the multiband Hubbard-I approximation to reproduce the multiplet features present in the experimental spectra. A comparison with available experimental data is made and the overall agreement is found to be good.
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| 11. |
- Lebègue, Sebastien, et al.
(författare)
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Multiplet effects in the electronic structure of light rare-earth metals
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:4, s. 045114-
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Tidskriftsartikel (refereegranskat)abstract
- The excited-state properties of the light rare-earth elemental metals praseodymium, neodymium, and samarium are studied within the Hubbard-I formalism. This method describes the multiplets of the rare-earth f shell by an exact diagonalization of the two-body part of the Hamiltonian. Subsequently, the rare-earth ion is embedded in the solid environment by incorporation of the atomic self-energy into a solid Green's function, which is calculated using the local density approximation to density functional theory. After describing the method briefly, a systematic comparison with available photoemission experiments is made, and it is found that all main structures of the experimental spectra are reproduced by the approach, with the exception of the features immediately below the Fermi level which are interpreted as a mark of a mechanism different from an atomiclike multiplet transition.
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| 12. |
- Lebègue, Sébastien, et al.
(författare)
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Quasiparticle and optical properties of BeH2
- 2007
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:3, s. 036223-
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Tidskriftsartikel (refereegranskat)abstract
- The quasiparticle and optical properties of BeH2 are computed by means of the all-electron GW approximation in conjunction with the projector augmented wave (PAW) method. The GW approximation, through the calculation of the self-energy and the optical dielectric function in the random phase approximation, shows that BeH2 is a large band gap insulator. The results are discussed in view of future experiments.
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| 13. |
- Lebegue, Sebastien, et al.
(författare)
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Semimetallic dense hydrogen above 260 GPa
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:25, s. 9766-9769
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Tidskriftsartikel (refereegranskat)abstract
- Being the lightest and the most abundant element in the universe, hydrogen is fascinating to physicists. In particular, the conditions of its metallization associated with a possible superconducting state at high temperature have been a matter of much debate in the scientific community, and progress in this field is strongly correlated with the advancements in theoretical methods and experimental techniques. Recently, the existence of hydrogen in a metallic state was reported experimentally at room temperature under a pressure of 260-270 GPa, but was shortly after that disputed in the light of more experiments, finding either a semimetal or a transition to an other phase. With the aim to reconcile the different interpretations proposed, we propose by combining several computational techniques, such as density functional theory and the GW approximation, that phase III at ambient temperature of hydrogen is the Cmca-12 phase, which becomes a semimetal at 260 GPa. From phonon calculations, we demonstrate it to be dynamically stable; calculated electron-phonon coupling is rather weak and therefore this phase is not expected to be a high-temperature superconductor.
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| 14. |
- Mao, Ho-Kwang, et al.
(författare)
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Electronic dynamics and plasmons of sodium under compression
- 2011
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:51, s. 20434-20437
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Tidskriftsartikel (refereegranskat)abstract
- Sodium, which has long been regarded as one of the simplest metals, displays a great deal of structural, optical, and electronic complexities under compression. We compressed pure Na in the body-centered cubic structure to 52 GPa and in the face-centered cubic structure from 64 to 97 GPa, and studied the plasmon excitations of both structures using the momentum-dependent inelastic X-ray scattering technique. The plasmon dispersion curves as a function of pressure were extrapolated to zero momentum with a quadratic approximation. As predicted by the simple free-electron model, the square of the zero-momentum plasmon energy increases linearly with densification of the body-centered cubic Na up to 1.5-fold. At further compressions and in face-centered cubic Na above 64 GPa, the linear relation curves progressively toward the density axis up to 3.7-fold densification at 97 GPa. Ab initio calculations indicate that the deviation is an expected behavior of Na remaining a simple metal.
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| 15. |
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| 16. |
- Ramzan, Muhammad, et al.
(författare)
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Electronic Structure from First-Principles of LiBH(4)center dot NH(3), Sr(NH(2)BH(3))(2), and Li(2)Al(BH(4))(5)center dot 6NH(3) for Hydrogen Storage Applications
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:40, s. 20036-20042
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Tidskriftsartikel (refereegranskat)abstract
- A series of compounds containing boron, nitrogen, and hydrogen atoms, namely, LiBH(4)center dot NH(3), Sr(NH(2)BH(3))(2), and Li(2)Al(BH(4))(5)center dot 6NH(3), were synthesized recently, and found to be promising for hydrogen storage. We have conducted the corresponding ab initio calculations using density functional theory and analyzed the corresponding electron density as well as derived properties. Also, molecular dynamics simulations were performed to study the diffusion of hydrogen in this series of compounds. We found that despite having widely different crystal structures and difference in their chemical composition, these compounds share common features at the level of their electronic structure. Moreover, diffusion of hydrogen appears to be more favorable in LiBH(4)center dot NH(3) than in Sr(NH(2)BH(3))(2) and Li(2)Al(BH(4))(5)center dot 6NH(3).
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| 17. |
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| 18. |
- Ramzan, Muhammad, 1971-, et al.
(författare)
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Hybrid Density Functional Calculations and Molecular Dynamics Study of Lithium Fluorosulphate, A Cathode Material for Lithium-Ion Batteries
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:5, s. 2600-2603
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we use hybrid density functional theory to calculate the electronic structure of lithium fluorosulphate (LiFeSO4F), which has been found recently to be an excellent cathode material for lithium-ion,batteries by Recham et al. (Nat. Mater. 2010, 9, 68). We calculate the average intercalation voltage of the corresponding battery, and we also analyze the electron charge distribution through Bader's analysis. Our results are in good agreement with the available experimental values. Then we studied the Li-diffusion in lithium fluorosulphate with ab initio molecular dynamics and found it to be three-dimensional.
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| 19. |
- Xu, Qichen
(författare)
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Computational and Algorithmic Approaches for Studying Exotic Spin Textures
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Exotic spin textures such as skyrmions, are proved to be promising candidates for the development of sustainable, next-generation spintronic devices. Despite extensive research in this domain, the quest for efficient computational methodologies for the automated discovery of novel functional magnetic materials, and identify the intricate topological spin textures they can host, remains a formidable challenge in solid-state physics. This thesis work introduces a promising end-to-end computational approach, employing the Heisenberg spin Hamiltonian model, aimed at overcoming this challenge and discovering novel exotic spin textures. Our approaches encompass an automated Density Functional Theory (DFT) calculation workflow designed to predict candidate functional magnetic materials for hosting spin textures, with those candidate material we calculate their magnetic exchange interactions for constructing the spin Hamiltonian. Subsequently, a computational workflow that integrates new developed metaheuristic optimization algorithms with Atomistic Spin Dynamics (ASD) simulations is employed to identify spin textures in targeted systems. Additionally, a post-processing tool for the visualization of these textures is presented.In the computational approach part of this work, we have developed several tools, including the high-throughput workflow code and the scientific visualization software, dedicated to studying exotic spin textures. On the algorithmic front, we introduce the metaheuristic conditional neural network and a controlled assembly approach for investigating the long-lifetime metastable states of magnetic systems with long-range interactions. Through these novel approaches, we have identified and predicted the constructing pathways to several novel high-order antiskyrmions and three types of skyrmionic metamaterials (i.e., lattice-like, flake-like, and cell-like). Furthermore, we applied evolutionary algorithms for identifying the ground states of skyrmionic systems, developing both the genetic tunneling optimizer (GTO) and a neuroevolutionary algorithm.In summary, the main results are:1. Discovery and analysis of the forming mechanism of novel high-order antiskyrmions in the PdFeIr system.2. Introduction of the evolutionary algorithm to the atomistic spin Hamiltonian model for the first time, combined with Markov chain Monte Carlo and atomistic spin dynamics simulations.3. Prediction of skyrmions in 4d and 5d doped B20 systems.4. Discovery and revealing the construction pathway of new skyrmionic textures, i.e., 2D skyrmionic metamaterials.5. Development of a general visualization and post-processing code for computational magnetism, which offers new opportunities for analyzing complex spin textures.
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