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: This work examines possible defect structures and their impact on the MoS2 monolayer electronic properties, using density functional theory in combination with scanning tunneling microscopy to identify the nature of the most likely defects.
Abstract: Monolayer MoS2 is a direct band gap semiconductor which has been recently investigated for low-power field effect transistors. The initial studies have shown promising performance, including a high on/off current ratio and carrier mobility with a high-κ gate dielectric. However, the performance of these devices strongly depends on the crystalline quality and defect morphology of the monolayers. In order to obtain a detailed understanding of the MoS2 electronic device properties, we examine possible defect structures and their impact on the MoS2 monolayer electronic properties, using density functional theory in combination with scanning tunneling microscopy to identify the nature of the most likely defects. Quantitative understanding based on a detailed knowledge of the atomic and electronic structures will facilitate the search of suitable defect passivation techniques. Our results show that S adatoms are the most energetically favorable type of defect and that S vacancies are energetically more favorable than Mo vacancies. This approach may be extended to other transition-metal dichalcogenides (TMDs), thus providing useful insights to optimize TMD-based electronic devices.
273 citations
TL;DR: In this paper, the thermal transport properties of hexagonal boron nitride (BN) based nanostructures are systematically studied using equilibrium molecular dynamics with a Tersoff-type empirical interatomic potential which is re-parametrized to represent experimental structure and phonon dispersion of two-dimensional hexagonal BN.
Abstract: Recent advances in the synthesis of hexagonal boron nitride (BN) based nanostructures, similar to graphene, graphene nanoribbons, and nanotubes, have attracted significant interest into characterization of these materials. While electronic and optical properties of BN-based materials have been widely studied, the thermal transport has not been thoroughly investigated. In this paper, the thermal transport properties of these BN nanostructures are systematically studied using equilibrium molecular dynamics with a Tersoff-type empirical interatomic potential which is re-parametrized to represent experimental structure and phonon dispersion of two-dimensional hexagonal BN. Our simulations show that BN nanostructures have considerably high thermal conductivities but are still quite lower than carbon-based counterparts. Qualitatively, however, the thermal conductivity of carbon and BN nanoribbons display similar behavior with respect to the variation of width and edge structure (zigzag and armchair). Additionally, thermal conductivities of $(10,10)$ and $(10,0)$ nanotubes, both carbon and BN, are found to have very weak dependence on their chirality.
273 citations
TL;DR: It is discovered that surface water on Cu plays a key role in the selectivity for hydrocarbon products over the oxygen-containing alcohol products by serving as a strong proton donor for electrochemical dehydration reductions.
Abstract: Practical environmental and energy applications of the electrochemical reduction of CO2 to chemicals and fuels require far more efficient and selective electrocatalysts beyond the only working material Cu, but the wealth of experimental data on Cu can serve to validate any proposed mechanisms. To provide design guidelines, we use quantum mechanics to predict the detailed atomistic mechanisms responsible for C1 and C2 products on Cu. Thus, we report the pH dependent routes to the major products, methane and ethylene, and identify the key intermediates where branches to methanol, ketene, ethanol, acetylene, and ethane are kinetically blocked. We discovered that surface water on Cu plays a key role in the selectivity for hydrocarbon products over the oxygen-containing alcohol products by serving as a strong proton donor for electrochemical dehydration reductions. We suggest new experiments to validate our predicted mechanisms.
273 citations
Max Planck Society1, Autonomous University of Madrid2, IMDEA3, Indiana University4, Spanish National Research Council5, Hong Kong University of Science and Technology6, Ruhr University Bochum7, Karlsruhe Institute of Technology8, Complutense University of Madrid9, École Polytechnique Fédérale de Lausanne10
TL;DR: It is shown that electron transfer at the interface between a metal surface and the organic electron acceptor tetracyano-p-quinodimethane leads to substantial structural rearrangements on both the organic and metallic sides of the interface.
Abstract: Organic/metal interfaces control the performance of many optoelectronic organic devices, including organic light-emitting diodes or field-effect transistors. Using scanning tunnelling microscopy, low-energy electron diffraction, X-ray photoemission spectroscopy, near-edge X-ray absorption fine structure spectroscopy and density functional theory calculations, we show that electron transfer at the interface between a metal surface and the organic electron acceptor tetracyano-p-quinodimethane leads to substantial structural rearrangements on both the organic and metallic sides of the interface. These structural modifications mediate new intermolecular interactions through the creation of stress fields that could not have been predicted on the basis of gas-phase neutral tetracyano-p-quinodimethane conformation.
272 citations
TL;DR: A dual protection strategy has been developed by nanocasting SiO2 into metal–organic frameworks to prepare high-loading SACs with excellent catalytic performance toward oxygen reduction and a general synthetic methodology toward high-content Sacs (such as FeSA, CoSA, NiSA).
Abstract: Single-atom catalysts (SACs) have sparked broad interest recently while the low metal loading poses a big challenge for further applications. Herein, a dual protection strategy has been developed to give high-content SACs by nanocasting SiO2 into porphyrinic metal–organic frameworks (MOFs). The pyrolysis of SiO2@MOF composite affords single-atom Fe implanted N-doped porous carbon (FeSA–N–C) with high Fe loading (3.46 wt%). The spatial isolation of Fe atoms centered in porphyrin linkers of MOF sets the first protective barrier to inhibit the Fe agglomeration during pyrolysis. The SiO2 in MOF provides additional protection by creating thermally stable FeN4/SiO2 interfaces. Thanks to the high-density FeSA sites, FeSA–N–C demonstrates excellent oxygen reduction performance in both alkaline and acidic medias. Meanwhile, FeSA–N–C also exhibits encouraging performance in proton exchange membrane fuel cell, demonstrating great potential for practical application. More far-reaching, this work grants a general synthetic methodology toward high-content SACs (such as FeSA, CoSA, NiSA). Single-atom catalysts (SACs) with high metal loading are highly desired to improve catalytic performance. Here, the authors report a dual protection strategy by nanocasting SiO2 into metal–organic frameworks to prepare high-loading SACs with excellent catalytic performance toward oxygen reduction.
272 citations
Cites background or methods from "From ultrasoft pseudopotentials to ..."
...The geometry optimization and electronic properties of the periodic structures are performed using the projector augmented wave (PAW) method implemented in the Vienna ab initio simulation package (VASP) code.(5-8) The generalized gradient...
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...(5) where id and ir are the disk and ring currents, respectively....
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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