| 1. |
- Chang, Yueqing, et al.
(författare)
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Downfolding from ab initio to interacting model Hamiltonians : comprehensive analysis and benchmarking of the DFT+cRPA approach
- 2024
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Ingår i: npj Computational Materials. - 2057-3960. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Model Hamiltonians are regularly derived from first principles to describe correlated matter. However, the standard methods for this contain a number of largely unexplored approximations. For a strongly correlated impurity model system, here we carefully compare a standard downfolding technique with the best possible ground-truth estimates for charge-neutral excited-state energies and wave functions using state-of-the-art first-principles many-body wave function approaches. To this end, we use the vanadocene molecule and analyze all downfolding aspects, including the Hamiltonian form, target basis, double-counting correction, and Coulomb interaction screening models. We find that the choice of target-space basis functions emerges as a key factor for the quality of the downfolded results, while orbital-dependent double-counting corrections diminish the quality. Background screening of the Coulomb interaction matrix elements primarily affects crystal-field excitations. Our benchmark uncovers the relative importance of each downfolding step and offers insights into the potential accuracy of minimal downfolded model Hamiltonians.
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| 2. |
- Romero, Aldo H., et al.
(författare)
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ABINIT: Overview and focus on selected capabilities
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 152:12
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Forskningsöversikt (refereegranskat)abstract
- abinit is probably the first electronic-structure package to have been released under an open-source license about 20 years ago. It implements density functional theory, density-functional perturbation theory (DFPT), many-body perturbation theory (GW approximation and Bethe-Salpeter equation), and more specific or advanced formalisms, such as dynamical mean-field theory (DMFT) and the "temperature-dependent effective potential" approach for anharmonic effects. Relying on planewaves for the representation of wavefunctions, density, and other space-dependent quantities, with pseudopotentials or projector-augmented waves (PAWs), it is well suited for the study of periodic materials, although nanostructures and molecules can be treated with the supercell technique. The present article starts with a brief description of the project, a summary of the theories upon which abinit relies, and a list of the associated capabilities. It then focuses on selected capabilities that might not be present in the majority of electronic structure packages either among planewave codes or, in general, treatment of strongly correlated materials using DMFT; materials under finite electric fields; properties at nuclei (electric field gradient, Mössbauer shifts, and orbital magnetization); positron annihilation; Raman intensities and electro-optic effect; and DFPT calculations of response to strain perturbation (elastic constants and piezoelectricity), spatial dispersion (flexoelectricity), electronic mobility, temperature dependence of the gap, and spin-magnetic-field perturbation. The abinit DFPT implementation is very general, including systems with van der Waals interaction or with noncollinear magnetism. Community projects are also described: generation of pseudopotential and PAW datasets, high-throughput calculations (databases of phonon band structure, second-harmonic generation, and GW computations of bandgaps), and the library libpaw. abinit has strong links with many other software projects that are briefly mentioned.
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| 3. |
- Wickramaratne, Darshana, et al.
(författare)
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Iron as a source of efficient Shockley-Read-Hall recombination in GaN
- 2016
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 109:16
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal impurities are known to adversely affect the efficiency of electronic and optoelectronic devices by introducing midgap defect levels that can act as efficient Shockley-Read-Hall centers. Iron impurities in GaN do not follow this pattern: their defect level is close to the conduction band and hence far from midgap. Using hybrid functional first-principles calculations, we uncover the electronic properties of Fe and we demonstrate that its high efficiency as a nonradiative center is due to a recombination cycle involving excited states. Unintentional incorporation of iron impurities at modest concentrations (10(15) cm(-3)) leads to nanosecond nonradiative recombination lifetimes, which can be detrimental for the efficiency of electronic and optoelectronic devices.
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| 4. |
- Zhang, Xie, et al.
(författare)
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First-principles calculations of defects and electron-phonon interactions : Seminal contributions of Audrius Alkauskas to the understanding of recombination processes
- 2024
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 135:15
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Tidskriftsartikel (refereegranskat)abstract
- First-principles calculations of defects and electron-phonon interactions play a critical role in the design and optimization of materials for electronic and optoelectronic devices. The late Audrius Alkauskas made seminal contributions to developing rigorous first-principles methodologies for the computation of defects and electron-phonon interactions, especially in the context of understanding the fundamental mechanisms of carrier recombination in semiconductors. Alkauskas was also a pioneer in the field of quantum defects, helping to build a first-principles understanding of the prototype nitrogen-vacancy center in diamond, as well as identifying novel defects. Here, we describe the important contributions made by Alkauskas and his collaborators and outline fruitful research directions that Alkauskas would have been keen to pursue. Audrius Alkauskas' scientific achievements and insights highlighted in this article will inspire and guide future developments and advances in the field.
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| 5. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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