DFT LDA Research Articles

Structural, electronic and optical studies of Sr2NiTeO6 double perovskite by first-principle DFT–LDA + U calculation

The structural, electronic and optical properties of monoclinic Sr2NiTeO6 double perovskite have been studied using corrected density functional theory–local density approximation with applying of Hubbard U corrected energy (DFT–LDA + U) method in plane-wave pseudopotential basis. The influence of on-site Coulomb interaction on structural, electronic and optical properties of Sr2NiTeO6 double perovskite compound, which consists of strongly localized Ni 3d electrons, were investigated. The highly Coulomb repulsion between electrons was corrected using Hubbard U parameter, varying from 0 to 8 eV for Ni 3d orbitals. The calculated results demonstrated that Sr2NiTeO6 double perovskite was sensitive to the change in U values. The optimized structural properties give a good agreement with experiment and other calculation data with lattice parameters a = 5.673 Å, b = 5.565 Å, c = 7.847 Å, α = 89.999°, β = 90.257° and γ = 90.000°. The DFT–LDA + U predicted the calculated electronic band structure of Sr2NiTeO6 was showed metallic behaviour (0 and 2 eV) and insulator behaviour (4, 6 and 8 eV). The density of state (DOS) shows that there was a significant effect on hybridization of Ni 3d and O 2p states at the conduction and valence band, respectively. Moreover, the results of optical studies such as dielectric function, absorption and reflectivity were found significant to the variation of U values applied indicates that the U values give a better description on the electronic localization of Ni 3d states.

Structural, electronic, and mechanical properties of anatase titanium dioxide

PurposeThe purpose of this paper is to analyze various properties of anatase titanium dioxide (TiO2) nanoparticles. Further, it proposes to implement Linear Combinations of Atomic Orbitals (LCAO) basis set under the framework of density functional theory and outline how LCAO is able to provide improved results in terms of various mechanical properties rather than plane wave and other theoretical results.Design/methodology/approachThis paper provides an exploratory study on anatase TiO2by implementing OLCAO–DFT–LDA–LBFGS–EOS–PZ algorithms to find out various ground-level properties. The data so obtained are complemented by various analysis using mathematical expressions, description of internal processes occurred and comparison to others’ analytical results.FindingsThe paper provides some empirical insights on how mechanical properties of anatase TiO2improved by implementing LCAO methodology. From the analysis of electronic properties, it is seen that the anatase TiO2supports the inter band indirect transition from O-2p in valence region to Ti-3d in the conduction region.Research limitations/implicationsMost of the electronic properties are underestimated because a single exchange-correlation potential is not continuous across the gap. This gap can be enhanced by implementing Green’s function in place of DFT and the other way is to implement self-interaction correction.Practical implicationsThe use of anatase TiO2is primarily used for catalytic applications. This is also used to enhance the quality of paper in the paper industry. Additionally, this is used as a prime ingredient in cosmetic industry.Originality/valueThis paper fulfills an identified need to study how LCAO, another basis set, plays an important role in improving material properties.

The extended stability range of phosphorus allotropes.

Phosphorus displays fascinating structural diversity and the discovery of new modifications continues to attract attention. In this work, a complete stability range of known and novel crystalline allotropes of phosphorus is described for the first time. This includes recently discovered tubular modifications and the prediction of not-yet-known crystal structures of [P12] nanorods and not-yet-isolated [P14] nanorods. Despite significant structural differences, all P allotropes consist of covalent substructures, which are held together by van der Waals interactions. Their correct reproduction by ab initio calculations is a core issue of current research. While some predictions with the established DFT functionals GGA and LDA differ significantly from experimental data in the description of the P allotropes, consistently excellent agreement with the GGA-D2 approach is used to predict the solid structures of the P nanorods.

G0W0 band structure of CdWO4

The full quasiparticle band structure of CdWO4 is calculated within the single-shot GW (G0W0) approximation using maximally localized Wannier functions, which allows one to assess the validity of the commonly used scissor operator. Calculations are performed using the Godby–Needs plasmon pole model and the accurate contour deformation technique. It is shown that while the two methods yield identical band gap energies, the low-lying states are given inaccurately by the plasmon pole model. We report a band gap energy of 4.94 eV, including spin–orbit interaction at the DFT–LDA (density functional theory–local density approximation) level. Quasiparticle renormalization in CdWO4 is shown to be correlated with localization distance. Electron and hole effective masses are calculated at the DFT and G0W0 levels.

Defect induced modification of the surface gap and optical properties of C(111)2 × 1 surface

AbstractTo resolve the long standing controversy between experimentally measured reflectance anisotropy (RA) of C(111)2 × 1 surface and theoretically calculated optical response, we demonstrated that defects at the C(111) surface in the form of minor hydrogen contamination, missing carbon atoms and/or terraces can be responsible for the appearance of the gap between the surface states, which is absent for the Pandey reconstructed ideal C(111)2 × 1. Ab initio DFT LDA calculations for such non‐ideal systems indeed demonstrate that even 6% of residual hydrogen (which is below the standard experimental detection limits) or 40 Å wide terraces are enough to sufficiently open the surface gap and account for the observed optical anisotropy.

Graphene and graphane functionalization with hydrogen: electronic and optical signatures

AbstractWe proved the possibility of electron gap tuning of graphene‐based materials, using extensive first principles modelling of the structural, electronic and optical properties of partially hydrogenated graphene. Optical tools were proposed to characterize the hydrogenation process. Sub‐monolayer hydrogen passivated graphene and various hydrogen induced superstructures were considered. Electron and optical DFT LDA gaps between 0.2 and 1.8 eV, suitable for microelectronic application, were obtained for low hydrogen coverage structures. For such systems, hydrogen clustering (by saturating neighbouring C dangling bonds at opposite sides of the graphene sheet) is energetically most favourable and generally produces a larger gap. A more homogeneous H distribution with one‐side bonding to C‐host atoms is, in contrast, less energetically favourable and even structurally unstable. In addition, such H configurations generally produce lower electron band gap. Hydrogen at low coverage not only locally buckles six‐fold carbon rings, it leads to dimerization and subsequent electron localization for neighbouring carbon atoms, which are not H bonded. Such structural and electronic processes are responsible for gap opening and its magnitude. Calculated linear optical response indicates that the optics is not only gap sensitive, but, combined with experimental spectra, can also provide access to microscopic properties of 2D nano‐sheets such as symmetry, hydrogen induced structure, degree of hydrogenation, chemical bonding, and others (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Partially Hydrogenated Graphene: Semiconductor Material with a Tunable Gap and Its Non-Destructive Optical Characterization

ABSTRACTWe report first principles modeling of partially hydrogenated graphene, with a variety of hydrogen induced superstructures. The dependence of the optical gap on hydrogen content and coverage is examined, to assess the best configurations suitable for optoelectronic applications. Electron and optical DFT LDA gaps in the range between 0.2 and 1.5 eV were obtained for low hydrogen coverage. For such systems, hydrogen clustering (by saturating neighbouring C dangling bonds at the opposite sides of the graphene sheet) is energetically most favourable and generally produces larger gap. More homogeneous H distribution one-side bonded to C-host atoms is, in contrast, less energetically favourable or even structurally unstable and generally produces smaller gap. In addition, ordering of hydrogen was observed at 50% of H, that offers a possibility of transforming 2D graphene to an array of 1D nanowires Calculated linear optical anisotropy and nonlinear second harmonic generation (this will be discussed in a forthcoming paper) indicate these are not only gap sensitive, but can provide an access to microscopic details of the 2D nano-sheets such as symmetry, hydrogen induced structure, degree of hydrogenation, chemical bonding and many others, all promising for device application. The approach developed can be used for graphene/ graphane single layer or bilayer, formed on top of various substrates, where experimental geometries may not provide conditions for complete hydrogenation of the 2D nano-sheet(s).

Stabilization of platinum nanoparticles on graphene by non-invasive functionalization

We have performed DFT–LDA calculations on the interaction of graphene with benzyl mercaptan, and on the role of the mercaptan in the adhesion of Pt nanoparticles. Our calculations indicate that Pt nanoparticles adhere more strongly to defect-free graphene than does benzyl mercaptan, which is essentially physisorbed. The role of the physisorbed mercaptan is to offer an abundance of –SH sites, to which the Pt bonding energy is greater than to graphene. This would lead to a higher deposition density of nanoparticles, which are decorated with chemisorbed mercaptan. The presence of benzyl mercaptan on the surfaces of Pt particles should also contribute to hindering the metallic phase coalescence.

Rhombohedral graphite: Comparative study of the electronic properties

Studies on rhombohedral graphite are often performed by exploiting the hexagonal P3 symmetry of its conventional cell. The primitive cell of that graphite, however, is rhombohedral, with an R 3 ¯ m symmetry. That difference in symmetry introduces variations in the electronic properties that we want to ascertain in this work. We used the CRYSTAL computational code to calculate the density of states DOS, electronic structure, electrostatic potential, and electric charge maps, with DFT–LDA, GGA, Hybrid, and Hartree–Fock Hamiltonians, as well as LDA–Perdew–Zunner and LDA–Vosko–Wilk–Nusair exchange-correlation potential pairs, the wave function being expanded in STO-6G and 6-31G basis sets. The hexagonal to rhombohedral deformation of the First Brillouin Zone produces modifications in the band structure, enhancing the theoretical semiconductor character of rhombohedral graphite when a rhombohedral unit cell is used. When a conventional hexagonal cell and Hartree–Fock Hamiltonians are used, the semimetal character of rhombohedral graphite is related to the inadequate self electron correlation and to the unit cell considered, the gap bands being more accentuated in the rhombohedral unit cell. Contour maps differences for different electronic properties under the different calculation conditions confirm the lamellar character of this graphite and the influence of the calculation conditions on the electronic properties.

Theoretical studies of structural and electronic properties of AlnAsn clusters

AbstractWe present theoretical results of size dependent structural, electronic, and optical properties of ligand‐free stoichiometric AlnAsn clusters of zinc‐blende modification. The investigation is done using a simplified parametrized linear combination of atomic orbital–density functional theory‐local density approximation–tight‐binding (LCAO–DFT–LDA–TB) method and consider clusters with n up to around 100. Initial structures have assumed as spherical parts of infinite zinc‐blende structure and then allowed to relax to the closest local‐energy‐minimum structure. We analyze the radial distributions of atoms, Mulliken populations, electronic energy levels (in particular, HOMO and LUMO), bandgap, and stability as a function of size and composition. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006

Ground-state properties and excitation energies of cubic SrO and MgO

Electronic ground-state properties and quasiparticle energies of the charge-transfer insulating oxides SrO and MgO have been computed. Structural properties calculations have been performed within DFT–LDA, while for the electronic excitations an efficient DFT–GW scheme, founded on the use of a model dielectric function, has been used. The comparison of our results with available theoretical and experimental data turns out to be satisfactory either for the ground state or for the excitation spectrum.

DFT–LDA study of NO adsorption on Rh(110) surface

We examine the interaction between NO and the Rh(110) surface using ab initio DFT–LDA pseudo-potential plane-wave total energy calculations. Four different adsorption sites for perpendicular NO are considered. The short-bridge site with linear NO is found to be the optimal adsorption configuration. It is also possible for NO to bond parallel to the surface, and this may be the precursor to NO dissociation.

Ab-initio adiabatic noble gas–metal interaction: the role of the induced polarization charge

Within an ab-initio DFT–LDA framework, we have investigated the polarization induced on He and Ne atoms by a jellium (Al-like) surface. It is shown that the displaced charge of the gas–metal system is spherically distributed around Ne. It is polarized instead for He with a dipole moment having the negative lobe towards the jellium surface. A relationship between the two different polarizations of He and Ne with corrugating and anti-corrugating behavior is discussed.

An analysis of molecular electrostatic potentials obtained by a local density functional approach

AbstractLocal density functional theory (DFT–LDA) has been explored as a tool for obtaining the molecular electrostatic potential V(r), using the code DMol. We have presented and discussed DFT–LDA electrostatic potentials for a representative series of molecules: ethylene, benzene, formamide, cytosine, and 2,3,7,8–tetrachlorodibenzo–p–dioxin. V(r) results obtained with a double numerical plus polarization (DNP) basis set show the key features that are characteristic of the ab initio potentials of these compounds and suggest that this is a useful approach, especially for large molecules that are difficult to study by ab initio methods.

CH Bond dissociation of acetylene: Local density functional calculations

AbstractThe CH bond dissociation energy of acetylene was computed by both ab initio approaches and density functional theory in a local density approximation (DFT–LDA). Structures and energies for acetylene and its dissociation products (the ethynyl and hydrogen radicals) are presented and compared. Using directly computed HCCH and HCC· energies and the exact H· value, the DFT–LDA calculations are found to yield CH dissociation energies ranging from 129 to 131 kcal/mol, in good agreement with recent experimental and the highest level theoretical results. The DFT–LDA results show little dependence upon the computational procedure used to obtain geometries.