Bernard Delley

THE GENERATION AND USE OF DELOCALIZED INTERNAL COORDINATES IN GEOMETRY OPTIMIZATION

Following on from the earlier work of Pulay and Fogarasi [J. Chem. Phys. 96, 2856 (1992)] we present an alternative definition of natural internal coordinates. This set of delocalized internal coordinates can be generated for any molecular topology, no matter how complicated, and is fully nonredundant. Using an appropriate Schmidt‐orthogonalization procedure, all standard bond length, bond angle, and dihedral angle constraints can be imposed within our internal coordinate scheme. Combinatorial constraints (in which sums or differences of stretches, bends, and torsions remain constant) can also be imposed. Optimizations on some fairly large systems (50–100 atoms) show that delocalized internal coordinates are far superior to Cartesians even with reliable Hessian information available at the starting geometry.

Binding energies, molecular structures, and vibrational frequencies of transition metal carbonyls using density functional theory with gradient corrections

The performance of the density functional theory (DFT) methods with different gradient corrections as an approach for the computation of transition metal complexes has been evaluated. As a test, the structures, binding energies, and vibrational frequencies of a series of binary transition metal carbonyl complexes were calculated. Comparison with previous studies shows that the gradient correction significantly improves the performance of the DFT schemes, and that the results obtained generally match the quality of the data obtained from coupled cluster and pair functional methods.

Dissociation of O2 at Al(111): the role of spin selection rules.

A most basic and puzzling enigma in surface science is the description of the dissociative adsorption of O(2) at the (111) surface of Al. Already for the sticking curve alone, the disagreement between experiment and results of state-of-the-art first-principles calculations can hardly be more dramatic. In this Letter we show that this is caused by hitherto unaccounted spin selection rules, which give rise to a highly nonadiabatic behavior in the O(2)/Al(111) interaction. We also discuss problems caused by the insufficient accuracy of present-day exchange-correlation functionals.

Stability and morphology of cerium oxide surfaces in an oxidizing environment: A first-principles investigation

We present density functional theory investigations of the bulk properties of cerium oxides (CeO2 and Ce2O3) and the three low index surfaces of CeO2, namely, (100), (110), and (111). For the surfaces, we consider various terminations including surface defects. Using the approach of “ab initio atomistic thermodynamics,” we find that the most stable surface structure considered is the stoichiometric (111) surface under “oxygen-rich” conditions, while for a more reducing environment, the same (111) surface, but with subsurface oxygen vacancies, is found to be the most stable one, and for a highly reducing environment, the (111) Ce-terminated surface becomes energetically favored. Interestingly, this latter surface exhibits a significant reconstruction in that it becomes oxygen terminated and the upper layers resemble the Ce2O3(0001) surface. This structure could represent a precursor to the phase transition of CeO2 to Ce2O3.

Giant lifetimes of optically excited states and the elusive structure of sodiumnitroprusside

The properties of sodiumnitroprusside (Na2[Fe(CN)5NO]*2H2O) are investigated by density functional theory. The calculated results both for the free anions as well as for the solid show that the ground-state Born–Oppenheimer surface has local minima for sidewards bonded and inverted NO. The calculated properties for the local minima: very long lifetime because of large barrier, diamagnetism, optical excitation energies, vibrational, and Mossbauer properties are in essential agreement with experiment. The present findings elucidate the possibility of population transfers by illumination with light of different wavelengths.

Ozone adsorption on carbon nanotubes: The role of Stone–Wales defects

First-principles calculations within the density functional theory have been performed in order to investigate ozone adsorption on carbon nanotubes. Particular emphasis is placed on the effects of Stone-Wales-like defects on the structural and electronic properties of (i) ideal tubes and (ii) tubes in the presence of ozone. Our results show that structural deformations induced on the pure carbon nanotubes by Stone-Wales defects are similar, as expected, to those induced on graphite; for the (10,0) tube, the semiconducting character is kept, though with a small reduction of the band gap. As for the ozone adsorption, the process on ideal nanotubes is most likely physisorption, though slightly stronger if compared to other previously studied molecules and consistent with the strong oxydizing nature of O(3). However, when ozone adsorbs on Stone-Wales defects, a strong chemisorption occurs, leading to relevant structural relaxations and to the formation of a CO covalent bond; this is consistent with experimental observations of CO functional groups, as well as of the liberation of CO gas phase and of the formation of C vacancies, thus explaining the consumption of the nanotube film upon ozone exposure.

Evidence for weak electronic correlations in iron pnictides

Using x-ray absorption and resonant inelastic x-ray scattering, charge dynamics at and near the Fe L edges is investigated in Fe pnictide materials, and contrasted to that measured in other Fe compounds. It is shown that the XAS and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar to Fe metal. Cluster diagonalization, multiplet, and density-functional calculations show that Coulomb correlations are much smaller than in the cuprates, highlighting the role of Fe metallicity and strong covalency in these materials. Best agreement with experiment is obtained using Hubbard parameters U <~;; 2eV and J ~;; 0.8eV.

Nonadiabatic potential-energy surfaces by constrained density-functional theory

Nonadiabatic effects play an important role in many chemical processes. In order to study the underlying nonadiabatic potential-energy surfaces (PESs), we present a locally constrained density-functional theory approach, which enables us to confine electrons to subspaces of the Hilbert space, e.g., to selected atoms or groups of atoms. This allows one to calculate nonadiabatic PESs for defined charge and spin states of the chosen subsystems. The capability of the method is demonstrated by calculating nonadiabatic PESs for the scattering of a sodium and a chlorine atom, for the interaction of a chlorine molecule with a small metal cluster, and for the dissociation of an oxygen molecule at the Al(111) surface.

Strong electron-phonon coupling in superconductingMgB2: A specific heat study

We report on measurements of the specific heat of the recently discovered superconductor MgB

THE EFFECT OF GRID QUALITY AND WEIGHT DERIVATIVES IN DENSITY FUNCTIONAL CALCULATIONS

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