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 results of an ab initio density-functional theory study of three bismuth-based multiferroics were presented, and the results showed that the application of the LDA+U$ method is essential to obtain realistic structural parameters for all three systems.
Abstract: We present results of an ab initio density-functional theory study of three bismuth-based multiferroics, $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$, ${\mathrm{Bi}}_{2}\mathrm{Fe}\mathrm{Cr}{\mathrm{O}}_{6}$, and $\mathrm{Bi}\mathrm{Cr}{\mathrm{O}}_{3}$. We disuss differences in the crystal and electronic structure of the three systems and show that the application of the $\mathrm{LDA}+U$ method is essential to obtain realistic structural parameters for ${\mathrm{Bi}}_{2}\mathrm{Fe}\mathrm{Cr}{\mathrm{O}}_{6}$. We calculate the magnetic nearest-neighbor coupling constants for all three systems and show how Anderson's theory of superexchange can be applied to explain the signs and relative magnitudes of these coupling constants. From the coupling constants we then obtain a mean-field approximation for the magnetic ordering temperatures. Guided by our comparison of these three systems, we discuss the possibilities for designing a multiferroic material with large magnetization above room temperature.
295 citations
TL;DR: In this paper, N-doped carbon-wrapped cobalt nanoparticles supported on Ndoped graphene nanosheets were prepared by a facile solvothermal procedure and subsequent calcination at controlled temperatures.
Abstract: Development of non-noble-metal catalysts for hydrogen evolution reaction (HER) with both excellent activity and robust stability has remained a key challenge in the past decades. Herein, for the first time, N-doped carbon-wrapped cobalt nanoparticles supported on N-doped graphene nanosheets were prepared by a facile solvothermal procedure and subsequent calcination at controlled temperatures. The electrocatalytic activity for HER was examined in 0.5 M H2SO4. Electrochemical measurements showed a small overpotential of only −49 mV with a Tafel slope of 79.3 mV/dec. Theoretical calculations based on density functional theory showed that the catalytically active sites were due to carbon atoms promoted by the entrapped cobalt nanoparticles. The results may offer a new methodology for the preparation of effective catalysts for water splitting technology.
295 citations
TL;DR: In this paper, density functional calculations are performed to explore magnetoelectric effects originating from the influence of an external electric field on magnetic properties of the Fe/MgO(001) interface.
Abstract: Density-functional calculations are performed to explore magnetoelectric effects originating from the influence of an external electric field on magnetic properties of the Fe/MgO(001) interface. It is shown that the effect on the interface magnetization and magnetocrystalline anisotropy can be substantially enhanced if the electric field is applied across a dielectric material with a large dielectric constant. In particular, we predict an enhancement of the interface magnetoelectric susceptibility by a factor of the dielectric constant of MgO over that of the free standing Fe (001) surface. We also predict a significant effect of electric field on the interface magnetocrystalline anisotropy due to the change in the relative occupancy of the 3d-orbitals of Fe atoms at the Fe/MgO interface. These results may be interesting for technological applications such as electrically controlled magnetic data storage.
295 citations
TL;DR: The quantum mechanical design and experimental realization of room-temperature polar metals in thin-film ANiO3 perovskite nickelates using a strategy based on atomic-scale control of inversion-preserving (centric) displacements is described and it is predicted that the geometric stabilization approach will provide novel avenues for realizing new multifunctional materials with unusual coexisting properties.
Abstract: Gauss's law dictates that the net electric field inside a conductor in electrostatic equilibrium is zero by effective charge screening; free carriers within a metal eliminate internal dipoles that may arise owing to asymmetric charge distributions. Quantum physics supports this view, demonstrating that delocalized electrons make a static macroscopic polarization, an ill-defined quantity in metals--it is exceedingly unusual to find a polar metal that exhibits long-range ordered dipoles owing to cooperative atomic displacements aligned from dipolar interactions as in insulating phases. Here we describe the quantum mechanical design and experimental realization of room-temperature polar metals in thin-film ANiO3 perovskite nickelates using a strategy based on atomic-scale control of inversion-preserving (centric) displacements. We predict with ab initio calculations that cooperative polar A cation displacements are geometrically stabilized with a non-equilibrium amplitude and tilt pattern of the corner-connected NiO6 octahedral--the structural signatures of perovskites--owing to geometric constraints imposed by the underlying substrate. Heteroepitaxial thin-films grown on LaAlO3 (111) substrates fulfil the design principles. We achieve both a conducting polar monoclinic oxide that is inaccessible in compositionally identical films grown on (001) substrates, and observe a hidden, previously unreported, non-equilibrium structure in thin-film geometries. We expect that the geometric stabilization approach will provide novel avenues for realizing new multifunctional materials with unusual coexisting properties.
294 citations
TL;DR: In this paper, the theoretical overpotential for the elementary steps involved in electrocatalytic oxygen evolution reaction (OER) on Co3O4(001) and β-CoOOH (0112) surfaces using density functional theory calculations (DFT).
Abstract: Co-based oxides are suitable electrode materials for the electrocatalytic oxygen evolution reaction (OER) with promising activity and stability, in addition to being widely available and relatively cheap. We investigate OER on Co3O4(001) and β-CoOOH (0112) surfaces using density functional theory calculations (DFT). We construct surface Pourbaix diagrams and investigate the theoretical overpotential for the elementary steps involved in OER on these surfaces. We show that inclusion of the Hubbard-U correction to DFT (DFT+U) is necessary to recover experimentally observed trends in the activity for the strongly correlated cobalt oxides. We find that the inclusion of the Hubbard-U correction lowers the activity of both Co3O4(001) and β-CoOOH(0112) when compared to results from pure DFT. In addition, the Hubbard-U correction shifts the location of Co3O4 and β-CoOOH from the strong binding leg to the weak binding leg of the OER volcano plot. The calculations also suggest that the theoretical overpotentials f...
292 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