Study of the structural and electronic properties of Zn1−x−yMgxTiyO structures

The reliability of the random phase approximation (RPA) and of σ-functional methods in conjunction with the mixed Gaussian and plane wave (GPW) basis set scheme as implemented in the CP2K package is investigated. First, based on the results for thermochemical properties of molecules and structural properties of crystalline solids, we establish reliable computational setups for practical calculations. Next, we compare the results obtained with these setups to those from standard GPW basis set approaches. For molecules, the results of RPA and σ-functional calculations within the GPW scheme are slightly worse, though still comparable, to those obtained using the standard Gaussian basis set scheme, provided a large enough orbital basis set is employed in the GPW calculations. Furthermore, the GPW calculations using σ-functionals are clearly more accurate than RPA calculations and even more so than those of conventional Kohn-Sham methods in the prediction of reaction energies and barrier heights for main group chemistry. For crystalline solids, the RPA and σ-functional methods significantly outperform the conventional Perdew-Burke-Ernzerhof (PBE) method in determining lattice constants. However, only the RPA method provides improved results for bulk moduli, while the σ-functional method yields errors comparable to those of the PBE method. A comparison of the results of the plane wave basis set calculations with the projector augmented wave method shows reasonable consistency for lattice constants and bulk moduli.

The reaction energies of 275 elementary reactions from the hydrocarbon combustion model GRI-Mech 3.0 were evaluated by electronic structure calculations using both localized Gaussian basis and plane wave basis sets. In the Gaussian basis calculations, the d-polarization function on C, N, and O elements reduces the mean absolute deviation (MAD) from the experimental value by 53%, a significant improvement in computational accuracy. In the plane wave basis calculation using different exchange-correlation (XC) functionals, the MAD values were 0.316-0.426 eV when non-hybrid type XC functionals such as RPBE, PBE, PW91, revPBE, and PBEsol were used. On the other hand, hybrid functionals like B3LYP and HSE06 reduced the MAD values significantly down to 0.182 and 0.233 eV, respectively. The B3LYP results have 49% less MAD compared to the PBE results. These demonstrated the strong advantage of the hybrid functional for calculating gas-phase reaction energies. The present comprehensive benchmarks will be crucial for future microkinetics as well as machine learning studies on the catalytic reactions. © 2019 Wiley Periodicals, Inc.

In this study, we used the co-precipitation method to synthesize Ti-doped ZnO nanoparticles having different Ti contents. We then used energy dispersive X-ray spectroscopy to perform an elemental analysis, which revealed that the Ti content varied in its atomic percentages from 5 at.%, 7 at.%, and 12 at.% to 16 at.%. We characterized the structural properties of the prepared samples using X-ray diffraction (XRD) spectroscopy and found Ti-doped ZnO to have an anatase structure in which the lattice parameters a = b and c decrease from 3.251 and 5.213 Å to 3.254 and 5.203 Å, respectively, when the Ti content increased from 5 at.% to 16 at.%. We also found the grain size of Fe-doped TiO2 to decrease from 12 nm to 10 nm with increasing Ti content. We characterized the molecular vibration of the samples using Fourier transform-infrared spectroscopy (FT-IR) and the optical properties using UV-Vis diffuse reflectance spectroscopy. The results show the band-gap energy of Ti-doped ZnO to decrease from 3.20 eV to 3.12 eV. We tested the photocatalytic activity of Ti-doped ZnO in the degradation of methylene blue from the aqueous solution under UV light irradiation and found the photocatalyst Ti-doped ZnO to have good degradation ability, with a degradation percentage of approximately 80 %.

This study demonstrates linear scaling with system size in fixednode diffusion QMC calculations with pseudopotentials for carbon fullerenes and for hydrogenated silicon clusters with nearly 1000 valence electrons. The range covered is C20 to C18o and SiH4 to Si211H140, The calculations were carried out with standard pseudopotentials (leaving four electrons per C or Si atom) and Slater Jastrow trial functions with orbitals from LDA density functional calculations. The key elements leading to linear scaling were constructions of sparse determinants and simplification of orbital functions. The LDA orbitals were obtained with a plane-wave basis set which was transformed to yield Wannier functions with maximum localization. These functions were then fitted to cubic spline expressions with a limited number of grid points and cut-off distances matching those of the plane-wave orbitals. The computational effort for evaluating trial functions of this type was clearly seen to behave in a linear fashion. Exploration of the effects of variation of cut-off radius revealed that energies, sensitive only to node structures, increased rapidly for cut-offs less than 7 bohr but were unaffected for cutoffs greater than 7 bohr. The accuracies of the calculations were checked in other ways. These included comparison calculations for SiH3 and Si5H12 using Gaussian, original plane-wave, and Wannier function basis sets which gave close agreement for energies.

The nature of the bonding of molecules to neutral gold atoms or surfaces is of wide interest, particularly with regard to recent molecular electronics experiments involving molecules linked to gold electrodes and nanoclusters. Here, the fundamental problem of accurate calculation of gold atom–ligand interactions is addressed, and a best-possible estimate for the binding energy of AuNH3 is obtained via coupled-cluster and density-functional calculations using series of Gaussian, Slater, and plane-wave basis sets. Poor convergence of both coupled-cluster and density-functional calculations toward the infinite basis-set limit is obtained from the Gaussian basis sets; using Slater basis sets, convergence is more rapid while plane-wave basis sets easily reached convergence. A total of 24 Gaussian basis sets are examined, and a method is introduced for determining if a particular basis set is sufficiently balanced in its treatment of the metal and its ligand. For balanced basis sets, better estimates of the binding energy are obtained neglecting corrections for basis-set superposition error. Various treatment of relativistic effects are examined including the use of relativistic effective core potentials (RECPs), ultrasoft pseudopotentials, and all electron scalar and full spin–orbit zero-order regular approximation calculations. While the use of RECPs has minimal affect, use of ultrasoft pseudopotentials and neglect of spin–orbit coupling both result in underestimation of the binding energy by 2–3 kcal mol−1 (15%–20%), as does the neglect of triples excitations in coupled-cluster theory. The PW91, B3LYP, BLYP, and LDA density functionals were investigated and of these only PW91 predicted binding energies and geometries in qualitative agreement with the coupled-cluster results. The AuNH3 complex is found to be a realistic model for the bonding of NH3 to a gold (111) surface, the primary differences being the prediction of charge transfer within the complex and associated significantly stronger binding. This may have profound implications for molecular electronics applications in which small gold clusters are used to represent macroscopic electrodes.

Effects of Ti-doped concentration on the microstructures and optical properties of ZnO thin films

Leucogranites are a characteristic feature of collisional orogens. Their generation is intimately related to crustal thickening and the active deformation and metamorphism of metapelites. Data from Proterozoic to present day orogenic belts show that collisional leucogranites (CLGs) are peraluminous, with muscovite, biotite and tourmaline as characteristic minerals. Isotopic ratios uniquely identify the metapelitic sequences in which CLGs occur as sources. Organic material in pelitic sources results in f O 2 in CLGs that is usually below the fayalite–magnetite–quartz buffer. Most CLGs form under vapour-poor conditions with melting involving a peritectic breakdown of muscovite. The low concentrations of Mg, Fe and Ti that characterize CLGs are largely related to biotite–melt equilibria in the source rocks. Concentrations of Zr, Th and rare earth elements are lower than expected from zircon and monazite saturation models because these minerals often remain enclosed in residual biotite during melting. Melting involving muscovite may limit the temperatures achieved in the source regions. A lack of nearby mantle heat sources in thick collisional orogens has led to thermal models for the generation of CLGs that involve flux melting, or large amounts of radiogenic heat generation, or decompression melting or shear heating, the last one emphasizing the link of leucogranites and their sources to crustal-scale shear zone systems.

PWDFT.jl: A Julia package for electronic structure calculation using density functional theory and plane wave basis

Microstructure refinement and mechanical properties improvement by developing IAF on inclusions in Ti–Al complex deoxidized HSLA steel

We introduced two methods to correct the singularity in the calculation of long-range Hartree-Fock (HF) exchange for long-range-corrected density functional theory (LC-DFT) calculations in plane-wave basis sets. The first method introduces an auxiliary function to cancel out the singularity. The second method introduces a truncated long-range Coulomb potential, which has no singularity. We assessed the introduced methods using the LC-BLYP functional by applying it to isolated systems of naphthalene and pyridine. We first compared the total energies and the HOMO energies of the singularity-corrected and uncorrected calculations and confirmed that singularity correction is essential for LC-DFT calculations using plane-wave basis sets. The LC-DFT calculation results converged rapidly with respect to the cell size as the other functionals, and their results were in good agreement with the calculated results obtained using Gaussian basis sets. LC-DFT succeeded in obtaining accurate orbital energies and excitation energies. We next applied LC-DFT with singularity correction methods to the electronic structure calculations of the extended systems, Si and SiC. We confirmed that singularity correction is important for calculations of extended systems as well. The calculation results of the valence and conduction bands by LC-BLYP showed good convergence with respect to the number of k points sampled. The introduced methods succeeded in overcoming the singularity problem in HF exchange calculation. We investigated the effect of the singularity correction on the excitation state calculation and found that careful treatment of the singularities is required compared to ground-state calculations. We finally examined the excitonic effect on the band gap of the extended systems. We calculated the excitation energies to the first excited state of the extended systems using a supercell model at the Γ point and found that the excitonic binding energy, supposed to be small for inorganic semiconductors, was quite large. Our findings suggest that more investigation on the effect of the excitonic binding energy on band gaps is necessary.

WTi is used as an adhesive layer in integrated circuit devices. The temperature dependent mechanical properties of WTi are still largely unexplored. In this paper we investigate WTi solid solutions with density functional theory calculations to determine the temperature and concentration dependent behavior of volume and coefficient of thermal expansion. The coefficient of thermal expansion is analyzed in terms of the bulk modulus, heat capacity, and Gr\"uneisen parameter. Furthermore, we gain insight into the bonding of the system via investigation of the electronic structure, phonon density of states, and analysis of the formation energy. Low Ti concentrations lead to strong W-Ti bonding, as manifested in additional high frequency peaks in the phonon density of states. As a consequence, deviations from Vegard's law are found at low Ti concentrations, with a minimum of the lattice constant at about 15 at. % Ti. The CTE as a function of Ti concentration shows a negative trend at low temperatures and Ti concentrations, which is related to a strong decrease of heat capacity. Finally we show that the Debye-Gr\"uneisen model yields results for WTi comparable to the quasiharmonic approach at a fraction of the computational cost.

This paper introduces two developments for the application of plane wave basis sets for accurate molecular calculations. (1) An analytical formula is introduced for the momentum space representation of a Coulomb operator truncated to a finite range. Using this operator, interactions between the molecule and its periodic replicas can be exactly eliminated. Examples demonstrating the accuracy of our scheme are given. Calculations using a good-quality plane wave basis yield variational total SCF energies which are lower than those obtained with the cc-pvQZ basis for simple two-electron systems. (2) A new mixed-basis augmented plane wave all-electron method, the plane wave core Gaussian method has been developed which expands the valence part of the molecular orbitals in plane waves, and the corelike part in nonoverlapping compact Gaussians. Analytic equations have been derived for the necessary mixed Gaussian/plane wave electron repulsion integrals. Using such augmented basis set, we were able to reproduce the Gaussian-basis Hartree energies of small molecules to within a few μEh.

The properties of Ti-doped ZnO films deposited by simultaneous RF and DC magnetron sputtering

Influence of Ti elements on the evolution of microstructure, mechanical properties and thermal stability of Al-Cu alloy

ZnO films with Ti atoms incorporated (TZO) in a wide range (0–18 at.%) have been grown by reactive co-sputtering on silicon and glass substrates. The influence of the titanium incorporation in the ZnO matrix on the structural and optical characteristics of the samples has been determined by Rutherford backscattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The results indicate that the samples with low Ti content (<4 at.%) exhibit a wurtzite-like structure, with the Ti4+ ions substitutionally incorporated into the ZnO structure, forming Ti-doped ZnO films. In particular, a very low concentration of Ti (<0.9 at.%) leads to a significant increase of the crystallinity of the TZO samples. Higher Ti contents give rise to a progressive amorphization of the wurtzite-like structure, so samples with high Ti content (≥18 at.%) display an amorphous structure, indicating in the XPS analysis, a predominance of Ti–O–Zn mixed oxides. The energy gap obtained from absorption spectrophotometry increases from 3.2 eV for pure ZnO films to 3.6 eV for those with the highest Ti content. Ti incorporation in the ZnO samples <0.9 at.% raises both the blue (380 nm) and green (approx. 550 nm) bands of the photoluminescence (PL) emission, thereby indicating a significant improvement of the PL efficiency of the samples.