This work assesses the Heyd-Scuseria-Ernzerhof (HSE) screened Coulomb hybrid density functional for the prediction of lattice constants and band gaps using a set of 40 simple and binary semiconductors. An extensive analysis of both basis set and relativistic effects is given. Results are compared with established pure density functionals. For lattice constants, HSE outperforms local spin-density approximation (LSDA) with a mean absolute error (MAE) of 0.037 A for HSE vs 0.047 A for LSDA. For this specific test set, all pure functionals tested produce MAEs for band gaps of 1.0–1.3 eV, consistent with the very well-known fact that pure functionals severely underestimate this property. On the other hand, HSE yields a MAE smaller than 0.3 eV. Importantly, HSE correctly predicts semiconducting behavior in systems where pure functionals erroneously predict a metal, such as, for instance, Ge. The short-range nature of the exchange integrals involved in HSE calculations makes their computation notably faster than regular hybrid functionals. The current results, paired with earlier work, suggest that HSE is a fast and accurate alternative to established density functionals, especially for solid state calculations.

Energy band gaps and lattice parameters evaluated with the Heyd-Scuseria-Ernzerhof screened hybrid functional.

In this review, high-resolution X-ray emission and X-ray absorption spectroscopy will be discussed. The focus is on the 3d transition-metal systems. To understand high-resolution X-ray emission and reso-nant X-ray emission, it is first necessary to spend some time discussing the X-ray absorption process. Section II discusses 1s X-ray absorption, i.e., the K edges, and section III deals with 2p X-ray absorption, the L edges. X-ray emission is discussed in, respectively, the L edges. X-ray emission is discussed in, respec-tively, and section V on 2p3s and 2p3d X-ray emission. Section VI focuses on magnetic dichroism effects, and in section VII selective X-ray absorption experiments are discussed. To limit the scope of this review paper, many related topics (for example, EELS, XPS, and resonant photoemission, phonon-oriented inelastic X-ray scat-tering, and X-ray microscopy) will not be discussed. In addition, many aspects of X-ray absorption, such as reflection experiments, diffraction absorption fine structure, and related experiments, will remain untouched. EXAFS will be discussed very briefly, and its X-ray emission analogue EXEFS 69,71 will not be discussed.

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High-Resolution X-ray Emission and X-ray Absorption Spectroscopy

Predicting and characterizing the crystal structure of materials is a key problem in materials research and development. We report the results of ab initio LDA/GGA computations for the following systems: AgAu, AgCd, AgMg, AgMo∗, AgNa, AgNb∗, AgPd, AgRh∗, AgRu∗, AgTc∗, AgTi, AgY, AgZr, AlSc, AuCd, AuMo∗, AuNb, AuPd, AuPt∗, AuRh∗, AuRu∗, AuSc, AuTc∗, AuTi, AuY, AuZr, CdMo∗, CdNb∗, CdPd, CdPt, CdRh, CdRu∗, CdTc∗, CdTi, CdY, CdZr, CrMg∗, MoNb, MoPd, MoPt, MoRh, MoRu, MoTc∗, MoTi, MoY ∗, MoZr, NbPd, NbPt, NbRh, NbRu, NbTc, NbY ∗, NbZr∗, PdPt, PdRh∗, PdRu∗, PdTc, PdTi, PdY, PdZr, PtRh, PtRu, PtY, PtTc, PtTi, PtZr, RhRu, RhTc, RhTi, RhY, RhZr, RuTi, RuTc, RuY, RuZr, TcTi, TcY, TcZr, TiZr∗, Y Zr∗ (∗= systems in which the ab initio method predicts that no compounds are stable). A detailed comparison to experimental data confirms the high accuracy with which ab initio methods can predict ground states.

Accuracy of ab initio methods in predicting the crystal structures of metals: A review of 80 binary alloys

The energy levels and local structures of Eu3+ incorporated in the lattice and surface sites of ZnO nanocrystals were investigated based on the high-resolution fluorescence spectra at 10 K. Radiative emissions from 5D1 were first observed for Eu3+ at the lattice site of ZnO. It is shown that the site symmetry of Eu3+ at the lattice site descends from C3v to Cs or C1, whereas Eu3+ ions at the surface occupy more disordered sites of the lowest symmetry C1. The luminescence decay of 5D0 at the lattice site, showing a rise time and longer lifetime, behaves distinctly from that of the surface sites. Because of a small filling factor (52%) of nanoparticles, the 5D0 lifetime of Eu3+ is significantly affected by the surrounding medium, which can be well interpreted with the virtual-cavity model. The Judd−Ofelt intensity parameters of Eu3+ in ZnO nanocrystals were determined, with Ω2,4,6 values of (9.59, 8.11, <0.25) and (21.51, 2.30, <0.25) in units of 10-20 cm2 for Eu3+ at the surface and lattice sites, respecti...

Optical Spectroscopy of Eu3+ Doped ZnO Nanocrystals

In an information management system, relevant policies are deployed to targets while policies which are not relevant are not. By deploying relevant policies, this reduces the amount of space requirements at the target to store the policies and the amount of data that needs to be sent to the target. Also, execution speed at the target may increase since the target does not need to evaluate policies that are not relevant.

Techniques and system to deploy policies intelligently

Electronic structure and structural phase stability in BaS, BaSe, and BaTe.

The linear muffin-tin-orbital method in its tight-binding representation is used to calculate the band structures and to investigate the structural phase stability of MgO, CaO, and SrO under high pressures. The calculated equilibrium properties agree well with the experimental data. In CaO and SrO, the B1-B2 transition occurs at 557 and 317 kbar, respectively, which are in agreement with the experimental observations. For MgO the transition from the B1 to B2 phase is found to occur at a very high pressure of 1975 kbar. The electronic band structures at normal and at high pressures and the variation of fundamental band gaps as a function of pressure are calculated.

Electronic and structural properties of alkaline-earth oxides under high pressure

A detailed description of the electronic band structures of MgS and MgSe were investigated using the tight binding linear muffintin orbital method. The calculations were done in the zinc blende (B3) and the NaCl-type (B1) structures. The calculated ground-state properties were found to be in agreement with the experimental values. Under compression both MgS and MgSe are found to undergo a structural phase transition from the B3 to the B1 structure at pressures of 377 and 317 kbar, respectively. At ambient conditions both MgS and MgSe are found to be indirect band gap semiconductors and exhibit the phenomenon of metallization at about 50% volume compression.

Electronic and structural properties of MgS and MgSe

From the first principles total energy calculations based on full-potential linear augmented plane wave method (FP-LAPW), the elastic properties of Al 2 X (X=Sc,Y,La,Lu) are reported here. Theoretical values of Young's modulus, shear modulus, Poisson's ratio and Debye temperature are estimated from the computed elastic constants. From the analysis of the ratio of shear to bulk modulus, it is found that these intermetallic compounds are brittle in nature. The calculated results are compared with other reported values.

FP-LAPW study of the elastic properties of Al2X (X=Sc,Y,La,Lu)

The electronic structure and structural properties of LaSb and LaBi are studied by means of the self-consistent tight binding linear muffin tin orbital method. The relative stabilities of LaSb and LaBi at high pressures in the Rock salt, Primitive tetragonal and CsCl structures are analysed. At compressed volumes, these compounds are found to favour the tetragonal phase rather the CsCl phase, which can be seen from the total energy curves. The transition from B1 to PT occurs around 8.6 and 11.2 GPa in LaSb and LaBi, respectively. The ground state properties of these compounds such as equilibrium lattice constant, bulk modulus are calculated and are in good agreement with the experimental results. The band structure and density of states are plotted for B1 and tetragonal phase and are compared with the available literature.

M. Rajagopalan

Papers

Electronic structure and structural phase stability in BaS, BaSe, and BaTe.

Electronic and structural properties of alkaline-earth oxides under high pressure

Electronic and structural properties of MgS and MgSe

FP-LAPW study of the elastic properties of Al2X (X=Sc,Y,La,Lu)

Electronic and structural properties of LaSb and LaBi