Correlation kinetic energy of many-electron systems: a modified Colle-Salvetti approach

The Colle and Salvetti approach [Theoret. Chim. Acta, 37, 329 (1975)] to the calculation of the correlation energy of a system is modified in order to explicitly include into the theory the kinetic contribution to the correlation energy. This is achieved by deducing from a many electrons wave function, including the correlation effects via a Jastrow factor, an approximate expression of the one-electron reduced density matrix. Applying the latter to the homogeneous electron gas, an analytic expression of the correlation kinetic energy is derived. The total correlation energy of such a system is then deduced from its kinetic contribution inverting a standard procedure. At variance of the original Colle-Salvetti theory, the parameters entering in both the kinetic correlation and the total correlation energies are determined analytically, leading to a satisfactory agreement with the results of Perdew and Wang [Phys. Rev. B 45, 13244 (1992)]. The resulting (parameter-free) expressions give rise to a modified-local-density approximation that can be used in self-consistent density-functional calculations. We have performed such calculations for a large set of atoms and ions and we have found results for the correlation energies and for the ionization potentials which improve those of the standard local-density approximation.Comment: 26 page

On the Short-Range Behavior of Correlated Pair Functions from the Adiabatic-Connection Fluctuation–Dissipation Theorem of Density-Functional Theory

The short-range behavior of correlated pair functions from the adiabatic-connection fluctuation–dissipation theorem (ACFD) of density functional theory (DFT) employing local exchange-correlation kernels has been analyzed. It has been found that for large basis sets the pair function exhibits unphysical humps for small interelectronic distances if the adiabatic local density approximation kernel is used in the ACFD scheme (this method is termed ACFD/ALDA in this work). However, up to basis set sizes of quadruple-ζ type quality, the correlated pair function of ACFD/ALDA behaves physically correct and the method yields reasonable results for atomization energies, ionization potentials, and intermolecular interaction energies. In order to correct the deficiencies of the pair function of ACFD/ALDA for large basis sets, a short-range correction scheme has been devised on the basis of a combination of the ACFD/ALDA pair function for the large distance regime with a proper physically correctly behaving pair function at smaller distances. While this approach, termed as ACFD/ALDAcorr, practically yields results close to those of the ACFD/ALDA method for finite basis sets, it enables basis set extrapolation techniques and thus can take dynamic correlation effects fully into account in contrast to the ACFD/ALDA approach. This work also presents an efficient density-fitting algorithm to compute the ACFD correlation energies that enables the calculation of correlation energies of extended molecular systems

Stahlstich-Sammlung nach den vorzüglichsten Gemälden der Dresdener Galerie.

L. C. copy bound in 2 volumes.Running title: Die Dresdener Galerie.Issued in 42 parts.Mode of access: Internet

Mechanisms of the Water-Gas Shift Reaction Catalyzed by Ruthenium Pentacarbonyl: A Density Functional Theory Study

The mechanism of the water-gas shift reaction catalyzed by Ru­(CO)₅ is analyzed using density functional methods in solution within the conductor-like screening model. Four different mechanistic pathways have been considered. It turned out that the incorporation of solvent effects is very important for a reasonable comparison among the mechanistic alternatives. The explicit inclusion of a water solvent molecule significantly changes the barriers of those steps which involve proton transfer in the transition state. The corresponding barriers are either lowered or increased, depending on the structure of the corresponding cyclic transition states. The results show that protolysis steps become competitive due to solution effects. The formation of formic acid as an intermediate in another, alternative pathway is also found to be competitive

New Insights into Ring-In-Ring Complexes of [<i>n</i>]Cycloparaphenylenes including the [12]Carbon Nanobelt

The supramolecular chemistry of cycloparaphenylenes (CPPs) is characterized by the ability of the ring system to undergo both concave and convex π–π interactions. As a consequence, ring-in-ring complexes can be formed in which the CPP serves as the host as well as the guest molecule ([n + x]CPP⊃[n]CPP). In this work, host–guest ring-in-ring complexes of [n]CPPs (n = 5–12) are investigated by means of electrospray ionization-tandem mass spectrometry (ESI-MS2) and laser desorption ionization mass spectrometry (LDI-MS). Extending the experimentally known complexes with ring size differences of five and six phenyl units (x = 5 and 6), we observe complexes with ring size differences of three up to seven phenyl units (x = 3–7). Energy-resolved collision experiments reveal that the charge is mainly located at the inner ring and complexes with phenyl unit differences of five and six are the most stable. In complexes featuring the same size difference, the complex stabilities slightly increase with an increasing size of the involved [n]CPPs. Utilizing the π-extended [12]carbon nanobelt ([12]CNB) as the guest also revealed an increase in complex stability. This study paves the way for a deeper understanding of the host–guest chemistry of CPPs

Density Functional Calculations and IR Reflection Absorption Spectroscopy on the Interaction of SO₂ with Oxide-Supported Pd Nanoparticles

A systematic study on the interaction of sulfur dioxide (SO2) on BaO-supported Pd nanoparticles has been carried out using suitable models and state-of-the-art density functional (DF) calculations. Detailed information concerning the structure and energetics of the different conformations of adsorbed SO2 is provided as a function of coverage together with calculated infrared reflection absorption spectroscopy (IRAS) spectra. SO2 may adsorb on Pd(111) in several conformations, some active, η2-SbOa and η1-Sb, and others inactive in IRAS, η3-SaOaOa. SO2 is found to attach stronger to Pd nanoparticle edges and corners, a fact intimately related to catalyst poisoning by site blocking. On Pd nanoparticles, SO2 is found to preferably adopt adsorption conformations that depend on the specific region on the nanoparticle, thus adding site specificity to vibrational recognition. Molecular beam experiments and IRAS have been performed on a single-crystal-based Pd/BaAl2xO1+3x/NiAl(110) model NOx storage and reduction catalyst and its individual components. SOx formation on the oxide components, evolution of a SO2 multilayer, and adsorption of SO2 on BaO or Pd nanoparticles is linked to DF calculations. The effect of cation intermixing in the oxide support and overlap of absorption bands on the unequivocal discrimination of signals are discussed

A Combined Density-Functional and IRAS Study on the Interaction of NO with Pd Nanoparticles: Identifying New Adsorption Sites with Novel Properties

Nanocrystalline particles expose special adsorption sites close to edges and corners, giving rise to novel adsorption and reaction properties. The spectroscopic identification of these sites represents a great challenge, however. Here, we present results of a combined experimental and theoretical study on the adsorption of NO on Pd nanoparticles, using infrared reflection absorption spectroscopy (IRAS) and calculations based on density-functional theory (DFT). This approach facilitates identification of the adsorption sites available on the nanoparticles and reveals detailed information on their bonding properties, on the vibrational parameters of NO adsorbed on these sites, and on their sequence of occupation. With respect to all these aspects, the adsorption behavior of NO on the Pd nanoparticles notably differs from any single crystal reference data available. The IRAS studies are performed on well-defined Pd nanoparticles supported on an ordered Al2O3 film on NiAl(110). The growth and structure of these particles has been characterized previously, predominately exposing (111) and a small fraction of (100) facets. Here, we systematically monitor the NO adsorption as a function of exposure in a temperature region between 100 and 300 K by means of time-resolved IRAS in combination with molecular beam (MB) dosing. We interpret these experimental data with the help of DFT calculations on the adsorption of NO on unsupported cuboctahedral Pdn clusters cut from Pd bulk and containing up to 140 atoms; for comparison, calculations of the reference adsorption complexes of NO on single-crystal Pd(111) surface have also been performed. NO molecules are shown to most favorably adsorb on hollow μ3-sites on (111) facets of Pdn clusters, closely followed by bridge μ2-sites at the edges between adjacent (111) facets. Both sites give rise to characteristic features in the vibrational spectrum and are populated sequentially. At higher coverage (and low temperature) on-top μ1-sites on the (111) facets begin to be occupied. At variance with the adsorption on Pd(111) surface, however, additional on-top-sites are available at the particle edges and corners, which reveal stronger NO adsorption. In spite of the strong adsorption in bridge (μ2) coordination geometry at edges, our calculations predict that intermolecular repulsion between adjacent μ2-NO species gives rise to the formation of mixed bridge/on-top structures at high coverage. Similarly to the bridge NO at particle edges, the edge- and corner-related μ1-NO species reveal characteristic vibrational frequencies, allowing for direct verification of this prediction by IRAS. The present results make possible the identification and monitoring of the occupation of specific sites on Pd nanoparticles by NO during adsorption and reaction processes

Chemical Fingerprints of Large Organic Molecules in Scanning Tunneling Microscopy: Imaging Adsorbate−Substrate Coupling of Metalloporphyrins

In this combined experimental and theoretical work we demonstrate at the example of tetraphenylporphyrins on Ag(111) how differences in individual adsorbate orbitals and their interaction with the substrate can be exploited to switch the appearance of the adsorbate in scanning tunneling microscopy (STM) experiments, such that electronically and chemically very similar large molecules become distinguishable in STM. In particular, an intermixed layer consisting of 2HTPP (TPP = tetraphenylporphyrin), CoTPP, and FeTPP molecules on Ag(111) was investigated, and it is demonstrated that STM images acquired with different bias voltages constitute fingerprints of the different molecules within the intermixed layer. By means of density functional calculations the observed features could be explained in detail and traced back to a direct orbital interaction of the adsorbed molecule with the surface. The explicit consideration of the surface in the calculations therefore turned out to be decisive to achieve good agreement with experiment