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 authors provide direct evidence to understand the origin of low thermal conductivity of lead chalcogenides using elastic measurements, which is attributed to the extremely weak Sn-Se atomic interactions (or bonds between layers).
Abstract: We provide direct evidence to understand the origin of low thermal conductivity of SnSe using elastic measurements. Compared to state-of-the-art lead chalcogenides $\mathrm{Pb}Q(Q=\mathrm{Te}$, Se, S), SnSe exhibits low values of sound velocity $(\ensuremath{\sim}1420\phantom{\rule{0.28em}{0ex}}\mathrm{m}/\mathrm{s})$, Young's modulus $(E\ensuremath{\sim}27.7\phantom{\rule{0.28em}{0ex}}\mathrm{GPa})$, and shear modulus $(G\ensuremath{\sim}9.6\phantom{\rule{0.28em}{0ex}}\mathrm{GPa})$, which are ascribed to the extremely weak Sn-Se atomic interactions (or bonds between layers); meanwhile, the deduced average Gr\"uneisen parameter \ensuremath{\gamma} of SnSe is as large as \ensuremath{\sim}3.13, originating from the strong anharmonicity of the bonding arrangement. The calculated phonon mean free path (l \ensuremath{\sim} 0.84 nm) at 300 K is comparable to the lattice parameters of SnSe, indicating little room is left for further reduction of the thermal conductivity through introducing nanoscale microstructures and microscale grain boundaries. The low elastic properties indicate that the weak chemical bonding stiffness of SnSe generally causes phonon modes softening which eventually slows down phonon propagation. This work provides insightful data to understand the low lattice thermal conductivity of SnSe.
260 citations
01 Feb 2020
TL;DR: In this paper, the authors present a materials processing strategy based on in situ electrodeposition of copper under CO2 reduction conditions that preferentially expose and maintain Cu(100) facets, which favor the formation of C2+ products.
Abstract: The electrosynthesis of C2+ hydrocarbons from CO2 has attracted recent attention in light of the relatively high market price per unit energy input. Today’s low selectivities and stabilities towards C2+ products at high current densities curtail system energy efficiency, which limits their prospects for economic competitiveness. Here we present a materials processing strategy based on in situ electrodeposition of copper under CO2 reduction conditions that preferentially expose and maintain Cu(100) facets, which favour the formation of C2+ products. We observe capping of facets during catalyst synthesis and achieve control over faceting to obtain a 70% increase in the ratio of Cu(100) facets to total facet area. We report a 90% Faradaic efficiency for C2+ products at a partial current density of 520 mA cm−2 and a full-cell C2+ power conversion efficiency of 37%. We achieve nearly constant C2H4 selectivity over 65 h operation at 350 mA cm−2 in a membrane electrode assembly electrolyser. Electrocatalytic reduction of CO2 to multicarbon products is useful for producing high-value chemicals and fuels. Here the authors present a strategy that is based on the in situ electrodeposition of copper under CO2 reduction conditions that preferentially expose and maintain Cu(100) facets, which favour the formation of C2+ products.
260 citations
TL;DR: The first experimental observation of a striking flatband near the Fermi level in the layered Fe_{3}Sn_{2} crystal consisting of two Fe kagome lattices separated by a Sn spacing layer is presented.
Abstract: A flatband representing a highly degenerate and dispersionless manifold state of electrons may offer unique opportunities for the emergence of exotic quantum phases To date, definitive experimental demonstrations of flatbands remain to be accomplished in realistic materials Here, we present the first experimental observation of a striking flatband near the Fermi level in the layered Fe_{3}Sn_{2} crystal consisting of two Fe kagome lattices separated by a Sn spacing layer The band flatness is attributed to the local destructive interferences of Bloch wave functions within the kagome lattices, as confirmed through theoretical calculations and modelings We also establish high-temperature ferromagnetic ordering in the system and interpret the observed collective phenomenon as a consequence of the synergetic effect of electron correlation and the peculiar lattice geometry Specifically, local spin moments formed by intramolecular exchange interaction are ferromagnetically coupled through a unique network of the hexagonal units in the kagome lattice Our findings have important implications to exploit emergent flat-band physics in special lattice geometries
260 citations
TL;DR: Agarwal et al. as mentioned in this paper report carbon nanotube-based materials with selected properties that exhibit enhanced thermoelectric performance, which are low-cost, versatile alternatives to more established inorganic ones.
Abstract: Organic thermoelectric materials are emerging as low-cost, versatile alternatives to more established inorganic ones. Avery et al. report carbon nanotube-based materials with selected properties that exhibit enhanced thermoelectric performance.
260 citations
TL;DR: It is shown that a nanostructured phase at lattice defects in CoCrNi causes its extraordinary properties, while it is magnetically frustrated and suppressed in CrMnFeCoNi.
Abstract: CrCoNi alloy exhibits a remarkable combination of strength and plastic deformation, even superior to the CrMnFeCoNi high-entropy alloy. We connect the magnetic and mechanical properties of CrCoNi, via a magnetically tunable phase transformation. While both alloys crystallize as single-phase face-centered-cubic (fcc) solid solutions, we find a distinctly lower-energy phase in CrCoNi alloy with a hexagonal close-packed (hcp) structure. Comparing the magnetic configurations of CrCoNi with those of other equiatomic ternary derivatives of CrMnFeCoNi confirms that magnetically frustrated Mn eliminates the fcc-hcp energy difference. This highlights the unique combination of chemistry and magnetic properties in CrCoNi, leading to a fcc-hcp phase transformation that occurs only in this alloy, and is triggered by dislocation slip and interaction with internal boundaries. This phase transformation sets CrCoNi apart from the parent quinary, and its other equiatomic ternary derivatives, and provides a new way for increasing strength without compromising plastic deformation.
259 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