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: Synthesis of atomically dispersed Rh on N-doped carbon is successfully synthesized and it is discovered that SA-Rh/CN exhibits promising electrocatalytic properties for formic acid oxidation and exhibits greatly enhanced tolerance to CO poisoning.
Abstract: To meet the requirements of potential applications, it is of great importance to explore new catalysts for formic acid oxidation that have both ultra-high mass activity and CO resistance. Here, we successfully synthesize atomically dispersed Rh on N-doped carbon (SA-Rh/CN) and discover that SA-Rh/CN exhibits promising electrocatalytic properties for formic acid oxidation. The mass activity shows 28- and 67-fold enhancements compared with state-of-the-art Pd/C and Pt/C, respectively, despite the low activity of Rh/C. Interestingly, SA-Rh/CN exhibits greatly enhanced tolerance to CO poisoning, and Rh atoms in SA-Rh/CN resist sintering after long-term testing, resulting in excellent catalytic stability. Density functional theory calculations suggest that the formate route is more favourable on SA-Rh/CN. According to calculations, the high barrier to produce CO, together with the relatively unfavourable binding with CO, contribute to its CO tolerance. Atomically dispersed Rh on N-doped carbon exhibits 28- and 67-fold enhancements compared with state-of-the-art Pd/C and Pt/C, despite the low activity of Rh/C. The Rh single atoms exhibit high tolerance to CO poisoning compared to Rh nanoparticles.
335 citations
TL;DR: In this paper, the behavior of carbon and nitrogen atoms in an iron-based solid solution is studied by ab initio density-functional-theory calculations, and the interaction of a C or a N atom in $\ensuremath{\alpha}$-Fe with a vacancy, other C or N interstitials as well as self-interstitial atoms is discussed and compared to known experimental results.
Abstract: The behavior of carbon and nitrogen atoms in iron based solid solution is studied by ab initio density-functional-theory calculations. The interaction of a C or a N atom in $\ensuremath{\alpha}$-Fe with a vacancy, other C or N interstitials as well as self-interstitial atoms is discussed and compared to known experimental results. The migration of these two foreign interstitial atoms is determined in pure Fe or when a vacancy is present in the supercell. According to our results, there is a strong binding energy of C or N with vacancies, whereas a repulsion is observed with self-interstitial atoms. Furthermore, a vacancy can trap up to two C, and a covalent bonding forms between the two C atoms. The situation is not as clear for N atoms, and a competition between the formation of N-V pairs and NN-V triplets is very probable.
335 citations
TL;DR: The successful design of lead-free direct band gap perovskite NCs with superior optical properties opens the door for high-performance lead-based optoelectronic devices.
Abstract: Lead-free double-perovskite nanocrystals (NCs), that is, Cs2AgInxBi1–xCl6 (x = 0, 0.25, 0.5, 0.75, and 0.9), that can be tuned from indirect band gap (x = 0, 0.25, and 0.5) to direct band gap (x = 0.75 and 0.9) are designed. Direct band gap NCs exhibit 3 times greater absorption cross section, lower sub-band gap trap states, and >5 times photoluminescence quantum efficiency (PLQE) compared to those observed for indirect band gap NCs (Cs2AgBiCl6). A PLQE of 36.6% for direct band gap NCs is comparable to those observed for lead perovskite NCs in the violet region. Besides the band edge violet emission, the direct band gap NCs exhibit bright orange (570 nm) emission. Density functional theory calculations suggesting forbidden transition is responsible for the orange emission, which is supported by time-resolved PL and PL excitation spectra. The successful design of lead-free direct band gap perovskite NCs with superior optical properties opens the door for high-performance lead-free perovskite optoelectronic...
335 citations
TL;DR: A composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte and shows significant potential for use in low-cost, high-performance fuel cells.
Abstract: The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizes the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells.
334 citations
TL;DR: In this paper, the authors quantitatively reproduce existing experimental data and present evidence that the apparent discrepancy between intensity ratios observed experimentally can be explained by the high sensitivity of the Raman-active modes to laser polarization.
Abstract: Raman spectra of MoS2, WS2, and their heterostructures are studied by density functional theory. We quantitatively reproduce existing experimental data and present evidence that the apparent discrepancy between intensity ratios observed experimentally can be explained by the high sensitivity of the Raman-active modes to laser polarization. Furthermore, MoS2/WS2 heterostructures up to four layers are considered in every possible combination and stacking order. Each heterostructure configuration possesses a unique Raman spectrum in both frequency and intensity that can be explained by changes in dielectric screening and interlayer interaction. The results establish a set of guidelines for the practical experimental identification of heterostructure configurations.
334 citations
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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