From ultrasoft pseudopotentials to the projector augmented-wave method
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.
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TL;DR: In this paper, the ambient temperature equations of state (EoS) of iron, cobalt, nickel, zinc, molybdenum, silver, platinum, and gold were measured by x-ray diffraction.
Abstract: The ambient temperature equations of state (EoS) of iron, cobalt, nickel, zinc, molybdenum, and silver have been measured by x-ray diffraction. These transition metals were compressed using diamond anvil cells with a helium pressure transmitting medium. The maximum pressure reached during these experiments varied between 65 GPa (for cobalt) and 200 GPa (for iron). This work completes previous measurements on six other metals [Phys. Rev. B 70, 094112 (2004)] to quantify the differences between ab initio calculations and experiment on a large experimental set of transition metals. The compression curves of iron, cobalt, nickel, zinc, molybdenum, silver, platinum, and gold are also calculated ab initio within the density-functional theory (DFT) formalism using the projector augmented-wave (PAW) method and different exchange-correlation functionals (LDA, GGA-PBE, GGA-PBEsol). The difference between PAW and available all-electron calculations is found to be negligible up to very high pressures. The success of each exchange-correlation functional is correlated with the atomic number. For all metals, the bulk modulus becomes overestimated at high pressure. In addition, this extended data set of metals' EoS enables to reduce further, but marginally, the systematic uncertainty of the high-pressure metrology based on the ruby standard.
368 citations
TL;DR: This report develops a simple and facile solid-state chemical reduction approach for a large-scale production of colored TiO2 at mild temperature (300-350 °C) and results indicate that valence band tail and vacancy band below the conduction band minimum appear for theTiO2-x, which implies that the TiO-x nanocrystal has a narrow band gap and therefore leads to a broad visible light absorption.
Abstract: Colored TiO2 has attracted enormous attention due to its visible light absorption and excellent photocatalytic activity. In this report, we develop a simple and facile solid-state chemical reduction approach for a large-scale production of colored TiO2 at mild temperature (300–350 °C). The obtained sample possesses a crystalline core/amorphous shell structure (TiO2@TiO2−x). The oxygen vacancy results in the formation of a disordered TiO2−x shell on the surface of TiO2 nanocrystals. XPS and theoretical calculation results indicate that valence band tail and vacancy band below the conduction band minimum appear for the TiO2−x, which implies that the TiO2@TiO2−x nanocrystal has a narrow band gap and therefore leads to a broad visible light absorption. Oxygen vacancy in a proper concentration promotes the charge separation of photogenerated carriers, which improves the photocatalytic activity of TiO2@TiO2−x nanocrystals. This facile and general method could be potentially used for large scale production of colored TiO2 with remarkable enhancement in the visible light absorption and solar-driven H2 production.
368 citations
Tsinghua University1, Beijing University of Technology2, East China University of Science and Technology3, University of Science and Technology of China4, Chinese Academy of Sciences5, Beijing University of Chemical Technology6, Sun Yat-sen University7, Queen's University Belfast8, Tianjin University of Technology9, University of California, Los Angeles10
TL;DR: A general host–guest strategy to make various single-atom catalysts on nitrogen-doped carbon has been developed; the iridium variant electrocatalyses the formic acid oxidation reaction with high mass activity and displays high tolerance to CO poisoning.
Abstract: Single-atom catalysts not only maximize metal atom efficiency, they also display properties that are considerably different to their more conventional nanoparticle equivalents, making them a promising family of materials to investigate. Herein we developed a general host–guest strategy to fabricate various metal single-atom catalysts on nitrogen-doped carbon (M1/CN, M = Pt, Ir, Pd, Ru, Mo, Ga, Cu, Ni, Mn). The iridium variant Ir1/CN electrocatalyses the formic acid oxidation reaction with a mass activity of 12.9 $${{{\rm{A}}\,{\rm{mg}}^{-1}_{{\rm{Ir}}}}}$$ whereas an Ir/C nanoparticle catalyst is almost inert (~4.8 × 10−3 $${{{\rm{A}}\,{\rm{mg}}^{-1}_{{\rm{Ir}}}}}$$). The activity of Ir1/CN is also 16 and 19 times greater than those of Pd/C and Pt/C, respectively. Furthermore, Ir1/CN displays high tolerance to CO poisoning. First-principle density functional theory reveals that the properties of Ir1/CN stem from the spatial isolation of iridium sites and from the modified electronic structure of iridium with respect to a conventional nanoparticle catalyst. Single-atom catalysts maximize metal atom efficiency and exhibit properties that can be considerably different to their nanoparticle equivalent. Now a general host–guest strategy to make various single-atom catalysts on nitrogen-doped carbon has been developed; the iridium variant electrocatalyses the formic acid oxidation reaction with high mass activity and displays high tolerance to CO poisoning.
367 citations
TL;DR: In this paper, the authors used photoemission spectroscopy and quantum transport to elucidate the topology of the room temperature magnet Co2MnGa and observed sharp bulk Weyl fermion line dispersions indicative of nontrivial topological invariants present in the magnetic phase.
Abstract: Topological matter is known to exhibit unconventional surface states and anomalous transport owing to unusual bulk electronic topology. In this study, we use photoemission spectroscopy and quantum transport to elucidate the topology of the room temperature magnet Co2MnGa. We observe sharp bulk Weyl fermion line dispersions indicative of nontrivial topological invariants present in the magnetic phase. On the surface of the magnet, we observe electronic wave functions that take the form of drumheads, enabling us to directly visualize the crucial components of the bulk-boundary topological correspondence. By considering the Berry curvature field associated with the observed topological Weyl fermion lines, we quantitatively account for the giant anomalous Hall response observed in this magnet. Our experimental results suggest a rich interplay of strongly interacting electrons and topology in quantum matter.
366 citations
TL;DR: In this article, the formations of intrinsic n-type defects, that is, oxygen vacancies and titanium interstitials, in rutile and anatase TiO2 have been compared using GGA+U calculations.
Abstract: The formations of intrinsic n-type defects, that is, oxygen vacancies and titanium interstitials, in rutile and anatase TiO2 have been compared using GGA+U calculations. In both crystal structures, these defects give rise to states in the band gap, corresponding to electrons localized at Ti3+ centers. O vacancy formation in rutile results in two excess electrons occupying 3d orbitals on Ti atoms neighboring the vacancy. Similarly, for anatase, two Ti 3d orbitals are occupied by the excess electrons, with one of these Ti sites neighboring the vacancy, and the second at a next-nearest Ti position. This localization is accompanied by one oxygen moving toward the vacancy site to give a “split vacancy” geometry. A second fully localized solution is also found for anatase, with both occupied Ti sites neighboring the vacancy site. This minimum is 0.05 eV less stable than the split vacancy and is thus expected to be present in experimental samples. A partially delocalized solution corresponding to the split vacan...
366 citations
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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