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Journal ArticleDOI

From ultrasoft pseudopotentials to the projector augmented-wave method

15 Jan 1999-Physical Review B (American Physical Society)-Vol. 59, Iss: 3, pp 1758-1775
TL;DR: In this paper, the formal relationship between US Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived and the Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional.
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.
Citations
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Journal ArticleDOI
TL;DR: Without the aid of external field or chemical modification, the metal-free half-metallicity predicted for narrow SiC zigzag nanoribbons opens a facile way for nanomaterial-based spintronics applications.
Abstract: Electronic structures of SiC nanoribbons have been studied by spin-polarized first-principles calculations. The armchair nanoribbons are nonmagnetic semiconductors, while the zigzag nanoribbons are magnetic metals. The spin polarization in the zigzag SiC nanoribbons is originated from the unpaired electrons localized on the ribbon edges. Interestingly, the zigzag nanoribbons narrower than ∼4 nm present half-metallic behavior. Without the aid of external field or chemical modification, the metal-free half-metallicity predicted for narrow SiC zigzag nanoribbons opens a facile way for nanomaterial-based spintronics applications.

223 citations

Journal ArticleDOI
TL;DR: In this paper, the electronic and magnetic properties of single 3D transition-metal (TM) atom (V, Cr, Mn, Fe, Co, and Ni) adsorbed graphdiyne (GDY) and graphyne (GY) are systematically studied using first-principles calculations within the density functional framework.
Abstract: The electronic and magnetic properties of single 3d transition-metal(TM) atom (V, Cr, Mn, Fe, Co, and Ni) adsorbed graphdiyne (GDY) and graphyne (GY) are systematically studied using first-principles calculations within the density functional framework. We find that the adsorption of TM atom not only efficiently modulates the electronic structures of GDY/GY system, but also introduces excellent magnetic properties, such as half-metal and spin-select half-semiconductor. Such modulation originates from the charge transfer between TM adatom and the GDY/GY sheet as well as the electron redistribution of the TM intra-atomic s, p, and d orbitals. Our results indicate that the TM adsorbed GDY/GY are excellent candidates for spintronics.

223 citations

Journal ArticleDOI
TL;DR: In this paper, the molecular level reaction pathway of converting hemicellulose-derived furfural to 2-methylfuran on a bifunctional Ru/RuOx/C catalyst using isopropyl alcohol as the hydrogen donor via a combination of isotopic labeling and kinetic studies was elucidated.
Abstract: Biomass conversion to fuels and chemicals provides sustainability, but the highly oxygenated nature of a large fraction of biomass-derived molecules requires removal of the excess oxygen and partial hydrogenation in the upgrade, typically met by hydrodeoxygenation processes. Catalytic transfer hydrogenation is a general approach in accomplishing this with renewable organic hydrogen donors, but mechanistic understanding is currently lacking. Here, we elucidate the molecular level reaction pathway of converting hemicellulose-derived furfural to 2-methylfuran on a bifunctional Ru/RuOx/C catalyst using isopropyl alcohol as the hydrogen donor via a combination of isotopic labeling and kinetic studies. Hydrogenation of the carbonyl group of furfural to furfuryl alcohol proceeds through a Lewis acid-mediated intermolecular hydride transfer and hydrogenolysis of furfuryl alcohol occurs mainly via ring-activation involving both metal and Lewis acid sites. Our results show that the bifunctional nature of the cataly...

223 citations

Journal ArticleDOI
22 Dec 2005-Nature
TL;DR: A novel simulation technique is used to identify a family of low-energy polytypic stacking-fault structures intermediate between the perovskite and post-perovskites phases, and identifies plane sliding involving the formation of stacking faults as the most favourable pathway for the phase transition.
Abstract: The post-perovskite phase of (Mg,Fe)SiO3 is believed to be the main mineral phase of the Earth's lowermost mantle (the D″ layer). Its properties explain1,2,3,4,5,6 numerous geophysical observations associated with this layer—for example, the D″ discontinuity7, its topography8 and seismic anisotropy within the layer9. Here we use a novel simulation technique, first-principles metadynamics, to identify a family of low-energy polytypic stacking-fault structures intermediate between the perovskite and post-perovskite phases. Metadynamics trajectories identify plane sliding involving the formation of stacking faults as the most favourable pathway for the phase transition, and as a likely mechanism for plastic deformation of perovskite and post-perovskite. In particular, the predicted slip planes are {010} for perovskite (consistent with experiment10,11) and {110} for post-perovskite (in contrast to the previously expected {010} slip planes1,2,3,4). Dominant slip planes define the lattice preferred orientation and elastic anisotropy of the texture. The {110} slip planes in post-perovskite require a much smaller degree of lattice preferred orientation to explain geophysical observations of shear-wave anisotropy in the D″ layer.

223 citations

Journal ArticleDOI
TL;DR: Comparison of experimental spectra and calculated vibrational modes enables confident assignment of most of the vibrational features between 50 and 3500 cm-1, and it is found that MAPbI3 shows exceptionally short phonon lifetimes, which can be linked to low lattice thermal conductivity.
Abstract: We present Raman and terahertz absorbance spectra of methylammonium lead halide single crystals (MAPbX3, X = I, Br, Cl) at temperatures between 80 and 370 K. These results show good agreement with density-functional-theory phonon calculations.1 Comparison of experimental spectra and calculated vibrational modes enables confident assignment of most of the vibrational features between 50 and 3500 cm-1. Reorientation of the methylammonium cations, unlocked in their cavities at the orthorhombic-to-tetragonal phase transition, plays a key role in shaping the vibrational spectra of the different compounds. Calculations show that these dynamics effects split Raman peaks and create more structure than predicted from the independent harmonic modes. This explains the presence of extra peaks in the experimental spectra that have been a source of confusion in earlier studies. We discuss singular features, in particular the torsional vibration of the C-N axis, which is the only molecular mode that is strongly influenced by the size of the lattice. From analysis of the spectral linewidths, we find that MAPbI3 shows exceptionally short phonon lifetimes, which can be linked to low lattice thermal conductivity. We show that optical rather than acoustic phonon scattering is likely to prevail at room temperature in these materials.

222 citations

References
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Book
31 Dec 1993
TL;DR: The linearized augmented planewave (LAPW) method has emerged as the standard by which density functional calculations for transition metal and rare-earth containing materials are judged.
Abstract: With its extreme accuracy and reasonable computational efficiency, the linearized augmented planewave (LAPW) method has emerged as the standard by which density functional calculations for transition metal and rare-earth containing materials are judged. This volume presents a thorough and self-conta

1,150 citations