Search results for "ORBIT"

Atomic and electronic structure of both perfect and nanostructured Ni(111) surfaces: First-principles calculations

2011

article i nfo In this study, we perform first principles simulations on both atomically smooth and nanostructured Ni(111) slabs. The latter contains periodically distributed nickel nanoclusters atop a thin metal film gradually growing from adatoms and serving as a promising catalyst. Applying the generalized gradient approximation within the formalism of the density functional theory we compare the atomic and electronic structures of Ni bulk, as well as both perfect and nanostructured (111) surfaces obtained using two different ab initio approaches: (i) the linear combination of atomic orbitals and (ii) the projector augmented plane waves. The most essential inter-atomic forces between the …

Localized molecular orbitals for excited states of polyenals, polyendials, and polyenones

2003

The work is focused on the generation of localized molecular orbitals for excited states. A recently developed a priori method based in a CAS-SCF–type algorithm is applied. The method generates directly localized orbitals and can be applied to multireference wavefunctions. A detailed description of the performance of the method as well as the locality of the MOs for the example of the singlet nπ* (CO) excited state is given. It is in general possible to obtain local orbitals for the doubly occupied and virtual valence orbitals. The partial delocalization of the π* (CO) orbital is discussed, as is the effect of the use of different CAS spaces. The systems under study are polyenals, polyendia…

Anion ordering and defect structure in Ruddlesden-Popper strontium niobium oxynitrides

2004

The crystal structure of the n = 1 member of the Ruddlesden-Popper family (SrO)(SrNbO(2)N)(n) was refined by the Rietveld method using neutron powder diffraction data. This complex crystallizes in the I4/mmm space group with cell parameters a = 4.0506(2) and c = 12.5936(9) angstroms. The refined composition was Sr(2)NbO(3.28)N(0.72), which corresponds to a formal oxidation state for Nb of +4.72, meaning 72% Nb(V) and 28% Nb(IV). The nitrogen atoms order in the equatorial sites of the niobium octahedra according to Pauling's second crystal rule as the more charged anion occupies the site showing the larger bond strength sums. Pauling's second crystal rule is shown to be able to predict the d…

N-benzoylindole-2,3-quinodimethane: Diels-Alder reactivity and synthetic applications for [b]annellated indoles

1991

Abstract The Diels-Alder reactivity of in situ generated N -benzoylindole-2,3-quinodimethane has been expanded considerably to include reactions with carbon- and hetero-dienophiles which furnish a variety of [ b ]annellated indoles as well as functionalized and annellated carbazoles. The frontier molecular orbital theory was found to be a useful model for the prediction of the experimental results under consideration of reactivity aspects.

Application of the open-shell size-consistent self-consistent singles and doubles configuration interaction method to multielectronic transitions in …

2000

The size-consistent self-consistent matrix dressing method has been applied on an open-shell single-configuration reference state. Once the reference state is converged, several low-lying roots can be obtained for the dressed configuration interaction (CI) matrices of appropriate symmetry. The CI matrices were built with a complete-active-space singles and doubles CI method in order to deal properly with multiconfiguration excited states. The vertical ionization and ionization–excitation transitions are obtained from the difference to the closed shell ground-state energy of the neutral molecule. The method has been applied to NH+3 and N+2 using atomic natural orbital basis sets and state-av…

A Discussion of Some Problems Associated with the Quantum Mechanical Treatment of Open-Shell Molecules

2003

Structures and EPR spectra of binary sulfur–nitrogen radicals from DFT calculations

2007

Abstract The scattered electron paramagnetic resonance (EPR) spectroscopic data for binary sulfur–nitrogen (S,N) radicals have been compiled and critically assessed.Many of these are inorganic rings or cages.For each species, possible equilibrium structures in the gas phase and the EPR hyperfine coupling (hfc) constants have been calculated with DFT using the B3LYP functional and basis sets of triple-ζ (or better) quality.Good agreement is obtained between calculated and measured values for the well characterized [S3N2]+ , a planar π-radical for which the s-component of the orbitals is likely to be reasonably independent of minor geometrical changes between gas-phase and condensed-phase sta…

Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes: Experimental and Theoretical Studies

2015

Previous time-resolved measurements on D149, the most-studied dye of the indoline family, had shown a fast time-component of 20–40 ps that had tentatively been attributed to structural relaxation. Using femtosecond transient absorption, we have investigated the isolated indoline donor unit (i.e., without acceptor group) and found an ultrafast decay characterized by two lifetimes of 3.5 and 23 ps. Density functional theory calculations show π-bonding and π*-antibonding character of the central ethylene group for the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The LUMO is localized on the flexible vinyl-diphenyl region of the donor unit and a twist…

Orbital-Resolved Partial Charge Transfer from the Methoxy Groups of Substituted Pyrenes in Complexes with Tetracyanoquinodimethane—A NEXAFS Study

2012

It is demonstrated that the near-edge X-ray absorption fine structure (NEXAFS) provides a powerful local probe of functional groups in novel charge transfer (CT) compounds and their electronic properties. Microcrystals of tetra-/hexamethoxypyrene as donors with the strong acceptor tetracyano-p-quinodimethane (TMP/HMP-TCNQ) were grown by vapor diffusion. The oxygen and nitrogen K-edge spectra are spectroscopic fingerprints of the functional groups in the donor and acceptor moieties, respectively. The orbital selectivity of the NEXAFS pre-edge resonances allows us to precisely elucidate the participation of specific orbitals in the charge transfer process. Upon complex formation, the intensit…

Calculations of the atomic structure of the KNbO3 (110) surface

2000

Abstract The O-terminated KNbO 3 (110) surface is modeled using a semi-empirical shell model and two different short-range interatomic potentials. We find this surface to be unstable with respect to a strong reconstruction and K-termination. This conclusion is confirmed by preliminary calculations using the ab initio linear combination of atomic orbitals (LCAO) formalism.