: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

This work reexamines the effect of the exchange screening parameter ω on the performance of the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional. We show that variation of the screening parameter influences solid band gaps the most. Other properties such as molecular thermochemistry or lattice constants of solids change little with ω. We recommend a new version of HSE with the screening parameter ω=0.11bohr−1 for further use. Compared to the original implementation, the new parametrization yields better thermochemical results and preserves the good accuracy for band gaps and lattice constants in solids.

Influence of the exchange screening parameter on the performance of screened hybrid functionals.

Zinc oxide is a unique material that exhibits semiconducting and piezoelectric dual properties. Using a solid–vapour phase thermal sublimation technique, nanocombs, nanorings, nanohelixes/nanosprings, nanobelts, nanowires and nanocages of ZnO have been synthesized under specific growth conditions. These unique nanostructures unambiguously demonstrate that ZnO probably has the richest family of nanostructures among all materials, both in structures and in properties. The nanostructures could have novel applications in optoelectronics, sensors, transducers and biomedical sciences. This article reviews the various nanostructures of ZnO grown by the solid–vapour phase technique and their corresponding growth mechanisms. The application of ZnO nanobelts as nanosensors, nanocantilevers, field effect transistors and nanoresonators is demonstrated.

/pdf/zinc-oxide-nanostructures-growth-properties-and-applications-8d5hcz3lg8.pdf

Zinc oxide nanostructures: growth, properties and applications

Point defects and impurities strongly affect the physical properties of materials and have a decisive impact on their performance in applications. First-principles calculations have emerged as a powerful approach that complements experiments and can serve as a predictive tool in the identification and characterization of defects. The theoretical modeling of point defects in crystalline materials by means of electronic-structure calculations, with an emphasis on approaches based on density functional theory (DFT), is reviewed. A general thermodynamic formalism is laid down to investigate the physical properties of point defects independent of the materials class (semiconductors, insulators, and metals), indicating how the relevant thermodynamic quantities, such as formation energy, entropy, and excess volume, can be obtained from electronic structure calculations. Practical aspects such as the supercell approach and efficient strategies to extrapolate to the isolated-defect or dilute limit are discussed. Recent advances in tractable approximations to the exchange-correlation functional ($\mathrm{DFT}+U$, hybrid functionals) and approaches beyond DFT are highlighted. These advances have largely removed the long-standing uncertainty of defect formation energies in semiconductors and insulators due to the failure of standard DFT to reproduce band gaps. Two case studies illustrate how such calculations provide new insight into the physics and role of point defects in real materials.

pdf/first-principles-calculations-for-point-defects-in-solids-i7sruaffv1.pdf

First-principles calculations for point defects in solids

Hybrid Fock exchange/density functional theory functionals have shown to be very successful in describing a wide range of molecular properties. For periodic systems, however, the long-range nature of the Fock exchange interaction and the resultant large computational requirements present a major drawback. This is especially true for metallic systems, which require a dense Brillouin zone sampling. Recently, a new hybrid functional [HSE03, J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003)] that addresses this problem within the context of methods that evaluate the Fock exchange in real space was introduced. We discuss the advantages the HSE03 functional brings to methods that rely on a reciprocal space description of the Fock exchange interaction, e.g., all methods that use plane wave basis sets. Furthermore, we present a detailed comparison of the performance of the HSE03 and PBE0 functionals for a set of archetypical solid state systems by calculating lattice parameters, bulk moduli, heats of formation, and band gaps. The results indicate that the hybrid functionals indeed often improve the description of these properties, but in several cases the results are not yet on par with standard gradient corrected functionals. This concerns in particular metallic systems for which the bandwidth and exchange splitting are seriously overestimated.

Screened hybrid density functionals applied to solids

On the prediction of band gaps from hybrid functional theory

The structure and surface energies of the cleaved, reconstructed, and fully hydroxylated (001) α-quartz surface of various thicknesses are investigated with periodic density functional theory (DFT). The properties of the cleaved and hydroxylated surface are reproduced with a slab thickness of 18 atomic layers, while a thicker 27-layer slab is necessary for the reconstructed surface. The performance of the hybrid DFT functional B3LYP, using an atomic basis set, is compared with the generalised gradient approximation, PBE, employing plane waves. Both methodologies give similar structures and surface energies for the cleaved and reconstructed surfaces, which validates studying these surfaces with hybrid DFT. However, there is a slight difference between the PBE and B3LYP approach for the geometry of the hydrogen bonded network on the hydroxylated surface. The PBE adsorption energy of CO on a surface silanol site is in good agreement with experimental values, suggesting that this method is more accurate for hydrogen bonded structures than B3LYP. New hybrid functionals, however, yield improved weak interactions. Since these functionals also give superior activation energies, we recommend applying the new functionals to contemporary issues involving the silica surface and adsorbates on this surface.

/pdf/structure-and-stability-of-the-001-a-quartz-surface-22uqkkok8j.pdf

Structure and stability of the (001) α-quartz surface

An ab initio study of ZnO(101̄0)

The structures of the (100) and the polar (111) surfaces of the rocksalt materials MgO and NiO have been studied using ab initio all electron total energy calculations, employing local basis sets, and a hybrid density functional (B3LYP). Various schemes for the stabilization of the polar surface have been examined, and we find that the hydroxylated (111) surfaces are more stable than the clean (100) surfaces. The computed energies suggest that the clean (111) surface of MgO is unstable with respect to faceting into (100) microfacets, while for the NiO(111) surface the octopolar reconstruction is favored. This distinction is due to the relatively high surface energy of the (100) surface of NiO.

/pdf/stability-of-rocksalt-polar-surfaces-an-ab-initio-study-of-zygj4uk4cx.pdf

Stability of rocksalt polar surfaces: An ab initio study of MgO(111) and NiO(111)

An ab-initio study of ZnO(112̄0)

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