Local Density Functional Theory Research Articles

On the Energetics of nh 3 Adsorption and Decomposition on nb(100) Surface : a ubi-qep Study

The energetics of the adsorption and decomposition of ammonia on Nb(100) surface was investigated by the method of unity bond index-quadratic exponential potential (UBI-QEP). The experimental as well as theoretically derived atomic heats of adsorptions were used as the input data and the results were compared with the findings of local density functional theory (LDFT) and non-local density functional theory (NLDFT). The method was capable of correctly predicting the fragmentation of ammonia on 4-fold hollow sites on the surface of Nb(100) and magnitudes of the heats of adsorptions and activation energies were more realistic.

The Structure of Gas Phase Tin Oxide Ions Generated by Laser Ablation: A Combined Fourier Transform Mass Spectrometry and Density Functional Theory Study

The radical ion series (SnO)+2-6, (SnO)−2-6, (SnO)0-5Sn+ and (SnO)1-6O− have been generated by the high power laser ablation of SnO and SnO2 targets positioned inside an ICR cell. In all ablation spectra obtained, and for any particular size Sn x core, the tin-rich clusters (SnO) x Sn+ were more abundant than the corresponding oxygen-equivalent clusters (SnO)+ x , while the oxygen-rich clusters (SnO) x O− were always more abundant than the oxygen-equivalent clusters (SnO)− x . High yields of the ions (SnO)1,3Sn+, (SnO)3,6O− and (SnO)−6 suggest high stabilities for these species. Low energy CID studies revealed that loss of neutral (SnO) x units is the preferred, and for most ions investigated the exclusive, dissociation pathway. Global minima for the smaller cations and anions are proposed on the basis of local density functional theory (DFT) calculations. Calculated dissociation energies for the neutral and charged clusters were found to compare well with effusion cell and FTICR results. DFT also predicts that, for any cluster with the same size Sn x core, IE(SnO) x EA(SnO) x . A correlation between ion abundances and DFT heats of formation is evident, and the ground state geometries provide insight into the evolution of structural versus size trends. Without assistance from the calculations, erroneous conclusions regarding the structures of the experimentally-sampled clusters might have been drawn from the low energy CID results.

Electron density calculations for MgCO3 using the sublattice technique

Self-consistent valence electron densities of a MgCO3 crystal and of its constituent sublattices are calculated on the basis of the local-density functional theory. The coupling between the sublattices is characterized by the density difference, introduced as the difference between the total electron density and the densities of individual sublattices. Intra-and interlattice hybridization effects are considered. It is shown that the density difference is in qualitative agreement with the experimental deformational density.

Oxidative corrosion of adhesive interlayers

The influence of excess oxygen on the interfacial bonding and adhesion at metal/ceramic boundaries was studied theoretically by means of electronic-structure calculations based on the local density functional theory. The model systems investigated were the weakly adhesive Ag(001)/MgAl2O4(001) interface and the interface Ag(001)/Ti/MgAl2O4(001), in which the reactive element Ti increases the strength of adhesion considerably. O insertion is exothermic at both interfaces due to a stabilising ion–ion interaction with the spinel surface. Ti reacts more readily than Ag even up to the formation of TiO. Ag shows a preference for Ag2O. However, the adhesion enhancement by the Ti interlayer is diminished by internal oxidation. The weak interaction at the pure Ag/spinel interface is almost unaffected by the oxidation.

P-type surface dopingof diamond: a first-principles study

Surface p-type conduction in diamond has been linked to anaqueous layer on a hydrogenated surface. We have used localdensity function theory to examine the electronic properties ofmolecular adsorbates on diamond surfaces. We find that a wide rangeof adsorbates are able to transfer an electron from the valence bandinto the molecule, facilitating hole conduction.

Substitutional cation impurities in α-Al 2O 3: ab-initio case study of segregation to the rhombohedral twin boundary

The energetics of substitutional cation impurities in the bulk volume and at the Σ7 ( 1 ̄ 012 ) rhombohedral twin boundary in alumina (α-Al 2O 3) were studied by means of ab-initio mixed-basis pseudopotential calculations based on the local density functional theory. For fifteen different substitutional cation impurity species, the positions of the impurity energy levels relative to the valence bands of the oxide were determined, and the type of bonding versus the atomic number of the impurity cation was analysed. For the rhombohedral twin boundary, increased propensity for segregation was found for impurity cations of large ionic radii for which an enhanced overlap between impurity and oxygen electronic states was observed. The effect of structural relaxation at the boundary was studied for the isovalent group-IIIB impurities Sc, Y and La. Segregation broke the screw-rotation symmetry of the pure, unsegregated boundary and altered the interface-plane termination.

Electrostatically Swollen Lamellar Stacks and Adiabatic Pair Potential of Highly Charged Platelike Colloids in an Electrolyte

We show that describing the screened electrostatic interactions in a periodic stack of rigid parallel identical charged platelike colloids within a local density functional theory approach generically leads to a swelling behavior. Within the same framework, we find that the effective potential between a pair of such plates immersed in an electrolyte is repulsive at all distances. This general result is in contradiction with a theory put forward by Sogami, Shinohara, and Smalley, that we criticize and thoroughly reconsider to show how the two approaches can be reconciled.

First-principles calculations for Li insertion into InSb

First-principles calculations are presented for the zinc-blende structure compound InSb, a candidate anode material for Li batteries. The atomic structure of InSb during Li insertion is discussed in the light of local density functional theory calculations based on plane-wave pseudopotential and linear muffin tin orbital methods.

Investigation of the bonding and magnetic properties of U3Cu4Ge4 and structurally related systems

Electronic and magnetic properties of the ferromagnets UCu2Ge2 (122), UGe2 (122), and of the newly found U3Cu4Ge4 (344) intermetallic system are self-consistently calculated within the local spin density functional theory using the augmented spherical wave (ASW) method. The influence of hybridisation on the chemical bonding and magnetic behaviour is discussed from the densities of states (DOS) as well as from the crystal orbital overlap population (COOP) leading to suggest comparative influences between electronic effects of the hybridisation as with respect to the structural changes when the constituents of (122) and (12) are built within U3Cu4Ge4. From the spin-only magnetic results the important contribution of the orbital effects is analysed.

Quantitative atomic-scale analysis of interface structures: transmission electron microscopy and local density functional theory.

Transmission electron microscopy (TEM) and local density functional theory (LDFT) are combined to analyze the microscopic structure of the rhombohedral twin interface in alpha-Al2O3. LDFT provides interfacial energetics and atomic and electronic structures for three competing models. With high-resolution TEM the atomic structure at the interface is imaged quantitatively along two orthogonal zone axes. Electron energy loss spectroscopy in TEM with nanoscale spatial resolution yields the interfacial electronic structure. Both experiments confirm the theoretically preferred model quantitatively.

X-ray crystal structures of alpha-KrF(2),[KrF][MF(6)](M=As,Sb,Bi),[Kr(2)F(3)][SbF(6).KrF(2), [Ke(2)F(3)2[SbF(6)]2.KrF(2), and [Kr(2)F(3)][AsF(6)].[KrF][AsF(6)]; synthesis and characterization of [Kr(2)F(3)][PF(6).nKrF(2); and theoretical studies of KrF(2), KrF+, Kr(2)F(3)+, and the [KrF][MF(6)](M=P,As,Sb,Bi) ion pairs.

The crystal structures of alpha-KrF(2) and salts containing the KrF(+) and Kr(2)F(3)(+) cations have been investigated for the first time using low-temperature single-crystal X-ray diffraction. The low-temperature alpha-phase of KrF(2) crystallizes in the tetragonal space group I4/mmm with a = 4.1790(6) A, c = 6.489(1) A, Z = 2, V = 113.32(3) A(3), R(1) = 0.0231, and wR(2) = 0.0534 at -125 degrees C. The [KrF][MF(6)] (M = As, Sb, Bi) salts are isomorphous and isostructural and crystallize in the monoclinic space group P2(1)/c with Z = 4. The unit cell parameters are as follows: beta-[KrF][AsF(6)], a = 5.1753(2) A, b = 10.2019(7) A, c = 10.5763(8) A, beta = 95.298(2) degrees, V = 556.02(6) A(3), R(1) = 0.0265, and wR(2) = 0.0652 at -120 degrees C; [KrF][SbF(6)], a = 5.2922(6) A, b = 10.444(1) A, c = 10.796(1) A, beta = 94.693(4) degrees, V = 594.73(1) A(3), R(1) = 0.0266, wR(2) = 0.0526 at -113 degrees C; [KrF][BiF(6)], a = 5.336(1) A, b = 10.513(2) A, c = 11.046(2) A, beta = 94.79(3) degrees, V = 617.6(2) A(3), R(1) = 0.0344, and wR(2) = 0.0912 at -130 degrees C. The Kr(2)F(3)(+) cation was investigated in [Kr(2)F(3)][SbF(6)].KrF(2), [Kr(2)F(3)](2)[SbF(6)](2).KrF(2), and [Kr(2)F(3)][AsF(6)].[KrF][AsF(6)]. [Kr(2)F(3)](2)[SbF(6)](2).KrF(2) crystallizes in the monoclinic P2(1)/c space group with Z = 4 and a = 8.042(2) A, b = 30.815(6) A, c = 8.137(2) A, beta = 111.945(2) degrees, V = 1870.1(7) A(3), R(1) = 0.0376, and wR(2) = 0.0742 at -125 degrees C. [Kr(2)F(3)][SbF(6)].KrF(2) crystallizes in the triclinic P1 space group with Z = 2 and a = 8.032(3) A, b = 8.559(4) A, c = 8.948(4) A, alpha = 69.659(9) degrees, beta = 63.75(1) degrees, gamma = 82.60(1) degrees, V = 517.1(4) A(3), R(1) = 0.0402, and wR(2) = 0.1039 at -113 degrees C. [Kr(2)F(3)][AsF(6)].[KrF][AsF(6)] crystallizes in the monoclinic space group P2(1)/c with Z = 4 and a = 6.247(1) A, b = 24.705(4) A, c = 8.8616(6) A, beta = 90.304(6) degrees, V = 1367.6(3) A(3), R(1) = 0.0471 and wR(2) = 0.0958 at -120 degrees C. The terminal Kr-F bond lengths of KrF(+) and Kr(2)F(3)(+) are very similar, exhibiting no crystallographically significant variation in the structures investigated (range, 1.765(3)-1.774(6) A and 1.780(7)-1.805(5) A, respectively). The Kr-F bridge bond lengths are significantly longer, with values ranging from 2.089(6) to 2.140(3) A in the KrF(+) salts and from 2.027(5) to 2.065(4) A in the Kr(2)F(3)(+) salts. The Kr-F bond lengths of KrF(2) in [Kr(2)F(3)][SbF(6)].KrF(2) and [Kr(2)F(3)](2)[SbF(6)](2).KrF(2) range from 1.868(4) to 1.888(4) A and are similar to those observed in alpha-KrF(2) (1.894(5) A). The synthesis and Raman spectrum of the new salt, [Kr(2)F(3)][PF(6)].nKrF(2), are also reported. Electron structure calculations at the Hartree-Fock and local density-functional theory levels were used to calculate the gas-phase geometries, charges, Mayer bond orders, and Mayer valencies of KrF(+), KrF(2), Kr(2)F(3)(+), and the ion pairs, [KrF][MF(6)] (M = P, As, Sb, Bi), and to assign their experimental vibrational frequencies.

Étude des structures électroniques de In2O3 pur et dopé avec l’étain

Abstract The electronic structures of the sesquioxide In 2 O 3 and Sn-doped In 2 O 3 are examined both self-consistently within the ab initio local density functional theory and using the non self-consistent extended Huckel method. A direct band gap and a wide dispersion of the bottom of the conduction band are obtained in the non-doped case. In the doped case, a narrow, half-filled band assigned to Sn is found at the bottom of the conduction band, in agreement with the metallic and transparent characteristics observed experimentally.

Self-consistent finite-difference electronic structure calculations

We present an accurate and efficient self-consistent method of solving the time-independent Schrödinger equation to find the electronic structure of materials. We use a finite-difference grid, which has the flexibility to cope with difficult geometry. The atomic cores are replaced with an embedded potential with a small muffin-tin radius allowing the full potential outside the muffin-tin. The resulting Hamiltonian matrix is sparse and can be diagonalized with computer time of O(N) using the Lanczos algorithm. For a larger number of atoms, the electronic properties of the system are found with greater efficiency than the Lanczos algorithm, using the calculation of the Green function of the system. Poisson's equation is solved using the multigrid method and the new potential in each self-consistent iteration is constructed within local density functional theory. The self-consistent electronic structure properties are shown for fcc copper.

Tight-binding model for transition metals: From cluster to solid

A transferable tight-binding (TB) model is presented within an orthogonal $\mathrm{spd}$ basis set that incorporates two-center intra-atomic parameters as well as local environment dependent on-site atomic energy levels. The parametrization of the model is determined by a simultaneous fit to the energy levels and total energies obtained from density-functional calculations for a number of cluster structures of up to 55 in size, although other bulk data could also be used in the fit. We have applied the method to rhodium and calculated the bulk properties. The equilibrium lattice constant, structural energy difference, elastic constants, surface energies, and vacancy formation energies are obtained and these are in reasonably good agreement with both bulk local-density functional theory and experiment. The two-center intra-atomic parameters are usually ignored in TB calculations. This paper demonstrates that it is essential that such terms be included in the calculation on clusters.

Multilayer relaxation of the Al(100) and Al(110) surfaces: an ab initio pseudopotential study

Abstract The multilayer relaxations of Al(100) and Al(110) surface are studied using the plane wave ab initio pseudopotential method within the local density functional theory. Our calculations show that the surface relaxation of Al(100) is an ‘anomalous’ outward relaxation, which is in excellent agreement with experimental results, although several previous empirical and semi-empirical theoretical studies have predicted contractions that are contrary to the experiments. For the Al(110) surface, our calculations do show inward relaxation, which is consistent with LEED experiments and other theoretical calculations. The origin of ‘inward’ and ‘outward’ relaxation is discussed. The surface energy is also studied in this work.

Electronic spin structure of novel persistent neutral radical with 1,3-diazaphenalene skeleton as studied by electron-nuclear magnetic resonance spectroscopies

Novel persistent neutral π-radical with 1,3-diazaphenalene skeleton has been isolated for the first time as crystalline solids. The cw-ESR spectra of the powder sample of 2,5,8-tri-tert-butyl-1,3-diazaphenalenyl (3) have been described by a triplet state with the spin Hamiltonian parameters of S = 1, g = 2.004, |D/hc|= 0.0167 cm -1 and |E/hc|< 10 -3 cm -1 . The temperature dependence of the triplet signal intensity was well described by a ground-state singlet dimer model with 2J/k B = -4.2 x 103 K. The similarity of the electronic structure to the parent hydrocarbon was derived from the observed parameters. The observed fine structure constants are interpreted on the basis of the two models with point dipole approximation. The degree of heteroatomic perturbation is evaluated from the π-spin density distribution obtained by local spin density functional theory.

Geometrical and electronic structure of Pd clusters on graphite

Pd clusters formed by physical vapor deposition at room temperature (RT) on highly oriented pyrolytic graphite were investigated by a combination of X-ray photoelectron spectroscopy and diffraction, angle-resolved ultraviolet photoelectron spectroscopy, scanning tunneling microscopy and calculations based on the local density functional theory. Different coverages with nominally 3, 5 and 10 Å were studied after deposition at RT and after heat treatment at 600°C. Local ordering exhibiting growth with an fcc(1 1 1) orientation is already observed at the lowest coverage, but with no preferred azimuthal orientation in accordance with the substrate itself. However electronic structure features characteristic for a Pd(1 1 1) single crystal appear only after heat treatment.

First-principles studies of the stability ofZintl ions in alkali-tin alloys: I. Crystalline intermetalliccompounds

The systematic variations of the crystal structure, phase stability,electronic structure and chemical bonding properties of equiatomicalkali-tin alloys as functions of the size of the alkali atom havebeen studied for the example of equiatomic alkali-tin alloys usingab initio local density calculations. It is demonstrated thatthe formation of the polyanionic phases of KSn and NaSn withtetrahedral Sn4 clusters may be interpreted within the Zintlprinciple: the large electronegativity difference leads to an atleast formally complete electron transfer from the alkali to the tinatoms and to the formation of strong covalent bonds stabilizing theSn44- `Zintl ions' which are isoelectronic and isostructuralto the P4 molecule. Charge transfer is also the dominantmechanism in LiSn; however, due to the smaller size of its alkaliion, the remaining intercluster interactions are too strong, so theSn ions form an extended network (in the form of corrugated planes)rather than isolated polyanions. The LiSn structure is alsodiscussed from the point of view of a simple ionic model such as isrealized in the CsCl structure. It is shown that the simple ionicmodel is destabilized by direct Sn-Sn interactions. Local densityfunctional theory is shown to provide an accurate description of thecomplex crystal structures of these alloys and a rationale for theobserved structural trends in alkali-group-IV alloys.

Microscopic structure and bonding at the Pd/SrTiO3 (001) Interface an ab-initio local-density-functional study

The microscopic structure and energetics of a SrTiO3 (001) surface covered with thin layers of Pd have been investigated by means of ab-initio electronic-structure calculations. A mixed-basis pseudopotential technique based on the local density functional theory was employed. Supercells containing SrTiO3 substrate slabs,with either SrO or TiO2 surface terminations, and Pd films of varying thicknesses were used to model the free (001) surfaces and the (001) heterophase interfaces. Based on the calculated energetics of adhesion for the different interfaces, the microscopic energetics of wetting and layer growth has been analysed. The TiO2 terminated substrate is energetically favourable for the adhesion of Pd films, with the Pdatoms bonded on top of the O atoms. The film adhesion is strongest for one (001) layer of fcc Pd and becomes weaker with increasing film thickness.

The Role of Sublattices in Chemical Bonding in Essentially Ionic Crystals

A technique for calculating the self-consistent electron density of sublattice and crystal as a whole has been developed based on the local electron density functional theory (DFT). Difference density, obtained by subtraction of the densities of the individual sublattices from the total electron density, is introduced as a quantity defining the relationship between the sublattices. Self-consistent calculations have been performed for series of compounds with a NaCl lattice: alkali and noble metal halides and alkali metal oxides and sulfides with an antifluorite lattice. As a result of these calculations, we formulated the key principle of chemical bonding based on sublattices. In the anion sublattice, alike atoms form a covalent type of bond with each other by transferring some portion of the charge to the interstice. The same mechanism of bonding is realized in sublattices of metal atoms containing the levels of the d-states in the valence region. In sublattices of simple metals, the valence density behaves as “metallic,” changing slightly within the unit cell, with electrons again moving from the metal sites into the interstice. Addition of the valence densities of sublattices leads to two essentially different situations: in one case, the metal sites coincide with the density maxima at the interstice of the anion sublattice, and in the other, they do not. In the first case, the superposition of the sublattice densities at the lattice sites leads to anion-cation hybridization, forming an essentially ionic chemical bond with a possible admixture of the covalent bond. In the second case, the anion sublattice is a covalently bonded framework incorporating the metal sublattice. This takes place in alkali metal oxides and sulfides.