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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
Yandong Ma1, Ying Dai1, Meng Guo1, Chengwang Niu1, Jibao Lu1, Baibiao Huang1 
TL;DR: The findings are a useful addition to the experimental studies of these new synthesized two-dimensional nanosheets, and suggest a new route to facilitate the design of spintronic devices for complementing graphene.
Abstract: Very recently, two-dimensional nanosheets of MoSe(2), MoTe(2) and WS(2) were successfully synthesized experimentally [Science, 2011, 331, 568]. In the present work, the electronic and magnetic properties of perfect, vacancy-doped, and nonmetal element (H, B, C, N, O, and F) adsorbed MoSe(2), MoTe(2) and WS(2) monolayers are systematically investigated by means of first-principles calculations to give a detailed understanding of these materials. It is found that: (1) MoSe(2), MoTe(2) and WS(2) exhibit surprising confinement-induced indirect-direct-gap crossover; (2) among all the neutral native vacancies of MoSe(2), MoTe(2) and WS(2) monolayers, only the Mo vacancy in MoSe(2) can induce spin-polarization and long-range antiferromagnetic coupling; (3) adsorption of nonmetal elements on the surface of MoSe(2), MoTe(2) and WS(2) nanosheets can induce a local magnetic moment; H-absorbed WS(2), MoSe(2), and MoTe(2) monolayers and F-adsorbed WS(2) and MoSe(2) monolayers show long-range antiferromagnetic coupling between local moments even when their distance is as long as ∼12 A. These findings are a useful addition to the experimental studies of these new synthesized two-dimensional nanosheets, and suggest a new route to facilitate the design of spintronic devices for complementing graphene. Further experimental studies are expected to confirm the attractive predictions.

403 citations

Journal ArticleDOI
TL;DR: In this paper, a multi-site H2 evolution reaction (HER) catalysts that minimize the water dissociation barrier and promote hydride coupling in neutral media is presented.
Abstract: High-performance hydrogen evolution reaction (HER) catalysts are compelling for the conversion of renewable electricity to fuels and feedstocks. The best HER catalysts rely on the use of platinum and show the highest performance in acidic media. Efficient HER catalysts based on inexpensive and Earth-abundant elements that operate in neutral (hence biocompatible) media could enable low-cost direct seawater splitting and the realization of bio-upgraded chemical fuels. In the challenging neutral-pH environment, water splitting is a multistep reaction. Here we present a HER catalyst comprising Ni and CrOx sites doped onto a Cu surface that operates efficiently in neutral media. The Ni and CrOx sites have strong binding energies for hydrogen and hydroxyl groups, respectively, which accelerates water dissociation, whereas the Cu has a weak hydrogen binding energy, promoting hydride coupling. The resulting catalyst exhibits a 48 mV overpotential at a current density of 10 mA cm−2 in a pH 7 buffer electrolyte. These findings suggest design principles for inexpensive, efficient and biocompatible catalytic systems. Integrating electrocatalytic H2 production with biological H2-fed systems for CO2 upgrading requires H2 generation to occur in biocompatible media—typically with neutral pH. Here, the authors design multi-site H2 evolution catalysts that minimize the water dissociation barrier and promote hydride coupling in neutral media.

403 citations

Journal Article
TL;DR: The creation and erasure of nanoscale conducting regions at the interface between two insulating oxides, LaAlO3 and SrTiO3 are reported.
Abstract: Experimental and theoretical investigations have demonstrated that a quasi-two-dimensional electron gas (q-2DEG) can form at the interface between two insulators: non-polar SrTiO3 and polar LaTiO3 (ref. 2), LaAlO3 (refs 3-5), KTaO3 (ref. 7) or LaVO3 (ref. 6). Electronically, the situation is analogous to the q-2DEGs formed in semiconductor heterostructures by modulation doping. LaAlO3/SrTiO3 heterostructures have recently been shown to exhibit a hysteretic electric-field-induced metal-insulator quantum phase transition for LaAlO3 thicknesses of 3 unit cells. Here, we report the creation and erasure of nanoscale conducting regions at the interface between two insulating oxides, LaAlO3 and SrTiO3. Using voltages applied by a conducting atomic force microscope (AFM) probe, the buried LaAlO3/SrTiO3 interface is locally and reversibly switched between insulating and conducting states. Persistent field effects are observed using the AFM probe as a gate. Patterning of conducting lines with widths of approximately 3 nm, as well as arrays of conducting islands with densities >10(14) inch(-2), is demonstrated. The patterned structures are stable for >24 h at room temperature.

402 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used first-principles calculations to identify active sites for the CO2 reduction reaction for Ag and Au metals, the two metals that have been shown to be the most active in producing CO.
Abstract: Highly active and selective CO2 conversion into useful chemicals is desirable to generate valuable products out of greenhouse gases. To date, various metal-based heterogeneous catalysts have shown promising electrochemical catalytic activities for CO2 reduction, yet there have been no systematic studies of the active sites of these metal catalysts that can guide further experiments. In this study, we use first-principles calculations to identify active sites for the CO2 reduction reaction for Ag and Au metals, the two metals that have been shown to be the most active in producing CO. We compare the catalytic activity and selectivity of three reaction sites of nanoparticles, namely, low-index surfaces, edge sites, and corner sites of these metals. For nanoparticle corner sites, in particular, we find that the size effect is critical, and 309-atom (or larger) nanoparticles should be used to appropriately describe realistic metal nanocatalysts. However, a 55-atom cluster model is often used in the literature...

402 citations

Journal ArticleDOI
TL;DR: In this paper, the trends in adsorption energy, geometry, vibrational properties, and other parameters derived from the electronic structure of the substrate were studied, and the influence of specific changes in their set-up, such as choice of the exchange correlation functional, the choice of pseudopotential, size of the basis set and substrate relaxation, has been carefully evaluated.
Abstract: We have studied the trends in CO adsorption on close-packed metal surfaces: Co, Ni, Cu from the 3d row, Ru, Rh, Pd, Ag from the 4d row and Ir, Pt, Au from the 5d row using density functional theory. In particular, we were concerned with the trends in adsorption energy, geometry, vibrational properties and other parameters derived from the electronic structure of the substrate. The influence of specific changes in our set-up, such as choice of the exchange correlation functional, the choice of pseudopotential, size of the basis set and substrate relaxation, has been carefully evaluated. We found that, while the geometrical and vibrational properties of the adsorbate–substrate complex are calculated with high accuracy, the adsorption energies calculated with the gradient-corrected Perdew–Wang exchange–correlation energies are overestimated. In addition, the calculations tend to favour adsorption sites with higher coordination, resulting in the prediction of the wrong adsorption sites for the Rh, Pt and Cu surfaces (hollow instead of top). The revised Perdew–Burke–Erzernhof functional (RPBE) leads to lower (i.e. more realistic) adsorption energies for transition metals, but to the wrong results for noble metals—for Ag and Au, endothermic adsorption is predicted. The site preference remains the same. We discuss trends in relation to the electronic structure of the substrate across the periodic table, summarizing the state-of-the-art of CO adsorption on close-packed metal surfaces.

402 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