Special points for brillouin-zone integrations
TL;DR: In this article, a method for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector is given, where the integration can be over the entire zone or over specified portions thereof.
Abstract: A method is given for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector. The integration can be over the entire Brillouin zone or over specified portions thereof. This method also has applications in spectral and density-of-state calculations. The relationships to the Chadi-Cohen and Gilat-Raubenheimer methods are indicated.
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TL;DR: This paper describes how accurate off-lattice ascent paths can be represented with respect to the grid points, and maintains the efficient linear scaling of an earlier version of the algorithm, and eliminates a tendency for the Bader surfaces to be aligned along the grid directions.
Abstract: A computational method for partitioning a charge density grid into Bader volumes is presented which is efficient, robust, and scales linearly with the number of grid points. The partitioning algorithm follows the steepest ascent paths along the charge density gradient from grid point to grid point until a charge density maximum is reached. In this paper, we describe how accurate off-lattice ascent paths can be represented with respect to the grid points. This improvement maintains the efficient linear scaling of an earlier version of the algorithm, and eliminates a tendency for the Bader surfaces to be aligned along the grid directions. As the algorithm assigns grid points to charge density maxima, subsequent paths are terminated when they reach previously assigned grid points. It is this grid-based approach which gives the algorithm its efficiency, and allows for the analysis of the large grids generated from plane-wave-based density functional theory calculations.
5,417 citations
TL;DR: In this paper, the 2D counterpart of layered black phosphorus, which is called phosphorene, is introduced as an unexplored p-type semiconducting material and the authors find that the band gap is direct, depends on the number of layers and the in-layer strain, and significantly larger than the bulk value of 0.31-0.36 eV.
Abstract: We introduce the 2D counterpart of layered black phosphorus, which we call phosphorene, as an unexplored p-type semiconducting material. Same as graphene and MoS2, single-layer phosphorene is flexible and can be mechanically exfoliated. We find phosphorene to be stable and, unlike graphene, to have an inherent, direct, and appreciable band gap. Our ab initio calculations indicate that the band gap is direct, depends on the number of layers and the in-layer strain, and is significantly larger than the bulk value of 0.31–0.36 eV. The observed photoluminescence peak of single-layer phosphorene in the visible optical range confirms that the band gap is larger than that of the bulk system. Our transport studies indicate a hole mobility that reflects the structural anisotropy of phosphorene and complements n-type MoS2. At room temperature, our few-layer phosphorene field-effect transistors with 1.0 μm channel length display a high on-current of 194 mA/mm, a high hole field-effect mobility of 286 cm2/V·s, and an...
5,233 citations
TL;DR: In this article, the tetragonal to orthorhombic ferroelastic phase transition between rutile- and CaCl-type phonon modes at high pressures is studied using first-principles calculations and the Landau free-energy expansion.
Abstract: The tetragonal to orthorhombic ferroelastic phase transition between rutile- and ${\text{CaCl}}_{2}$-type ${\text{SiO}}_{2}$ at high pressures is studied using first-principles calculations and the Landau free-energy expansion. The phase transition is systematically investigated in terms of characteristic phonon modes with ${\text{B}}_{1g}$ and ${\text{A}}_{g}$ symmetries, shear moduli, transverse-acoustic mode, rotation angle of the ${\text{SiO}}_{6}$ octahedra, spontaneous symmetry-breaking and volume strains, and enthalpy. The results show that these physical behaviors at the transition are well described using the Landau free-energy expansion parametrized by the first-principles calculations.
4,196 citations
TL;DR: In this article, a few-layer phosphorene has been introduced as a 2D p-type material for electronic applications, which has an inherent, direct and appreciable band gap that depends on the number of layers.
Abstract: Preceding the current interest in layered materials for electronic applications, research in the 1960's found that black phosphorus combines high carrier mobility with a fundamental band gap. We introduce its counterpart, dubbed few-layer phosphorene, as a new 2D p-type material. Same as graphene and MoS2, phosphorene is flexible and can be mechanically exfoliated. We find phosphorene to be stable and, unlike graphene, to have an inherent, direct and appreciable band-gap that depends on the number of layers. Our transport studies indicate a carrier mobility that reflects its structural anisotropy and is superior to MoS2. At room temperature, our phosphorene field-effect transistors with 1.0 um channel length display a high on-current of 194 mA/mm, a high hole field-effect mobility of 286 cm2/Vs, and an on/off ratio up to 1E4. We demonstrate the possibility of phosphorene integration by constructing the first 2D CMOS inverter of phosphorene PMOS and MoS2 NMOS transistors.
3,846 citations
TL;DR: An unprecedented ZT of 2.6 ± 0.3 at 923 K is reported in SnSe single crystals measured along the b axis of the room-temperature orthorhombic unit cell, which highlights alternative strategies to nanostructuring for achieving high thermoelectric performance.
Abstract: The thermoelectric effect enables direct and reversible conversion between thermal and electrical energy, and provides a viable route for power generation from waste heat The efficiency of thermoelectric materials is dictated by the dimensionless figure of merit, ZT (where Z is the figure of merit and T is absolute temperature), which governs the Carnot efficiency for heat conversion Enhancements above the generally high threshold value of 25 have important implications for commercial deployment, especially for compounds free of Pb and Te Here we report an unprecedented ZT of 26 ± 03 at 923 K, realized in SnSe single crystals measured along the b axis of the room-temperature orthorhombic unit cell This material also shows a high ZT of 23 ± 03 along the c axis but a significantly reduced ZT of 08 ± 02 along the a axis We attribute the remarkably high ZT along the b axis to the intrinsically ultralow lattice thermal conductivity in SnSe The layered structure of SnSe derives from a distorted rock-salt structure, and features anomalously high Gruneisen parameters, which reflect the anharmonic and anisotropic bonding We attribute the exceptionally low lattice thermal conductivity (023 ± 003 W m(-1) K(-1) at 973 K) in SnSe to the anharmonicity These findings highlight alternative strategies to nanostructuring for achieving high thermoelectric performance
3,823 citations