Time filter

Source Type

Aubiere, France

The exact formulation of multi-configuration density-functional theory is discussed in this work. As an alternative to range-separated methods, where electron correlation effects are split in the coordinate space, the combination of configuration interaction methods with orbital occupation functionals is explored at the formal level through the separation of correlation effects in the orbital space. When applied to model Hamiltonians, this approach leads to an exact site-occupation embedding theory (SOET). An adiabatic connection expression is derived for the complementary bath functional and a comparison with density matrix embedding theory is made. Illustrative results are given for the simple two-site Hubbard model. SOET is then applied to a quantum chemical Hamiltonian, thus leading to an exact complete active space site-occupation functional theory (CASSOFT) where active electrons are correlated explicitly within the CAS and the remaining contributions to the correlation energy are described with an orbital occupation functional. The computational implementation of SOET and CASSOFT as well as the development of approximate functionals are left for future work. © 2015 © 2015 Taylor & Francis. Source

Boutinaud P.,National Graduate School of Chemistry of Clermont Ferrand | Boutinaud P.,CNRS Institute of Chemistry
Inorganic Chemistry | Year: 2013

A model is introduced to predict the energy of metal-to-metal charge-transfer transitions in oxide compounds containing Bi3+ ions and d0 or d10 metals (Mn+). The model takes into account the structural characteristics of the host lattices, the anion relaxation resulting from Bi3+ doping, and the electronegativities and coordination numbers of the Bi3+ and Mn+ ions in the compounds. It is shown, through a critical review of the archival literature, that this model provides new insights on the assignment of the luminescence spectra and the related interpretation of the spectroscopic behaviors. © 2013 American Chemical Society. Source

Alam M.M.,CNRS Institute of Chemistry
Physical Chemistry Chemical Physics | Year: 2014

In the present work, we address the question-"which among the electron donors and the electron acceptors contribute more to the two-photon (TP) activity of a donor-π-acceptor type of molecule?" For this purpose we have performed ab initio calculations to calculate the TP transition probability (δTP) of a recently synthesized (Benedetti et al., J. Am. Chem. Soc., 2012, 134(30), 12418-12421) cyclopenta[b]naphthalene based chemo-sensor and its derivatives containing different electron donor and acceptor groups. Our study revealed that both under vacuum and in solvent phases, an increase in electron donor strength (-OMe, -NH2, -NMe2) increases the δTP value up to five times, whereas, an increase in the acceptor group strength (-COCH3, -NO2, -CN) increases it by a factor of two only. The highest δTP value is obtained for the molecule having the strongest donor-acceptor pair (-CN, -NMe2) considered in this work. We have also noted that, the removal of the cyclopentane ring from the original system increases the δTP value by ∼20% and the replacement of the naphthyl group by the benzene ring decreases it by ∼70%. All these results are explained by inspecting different TP tensor elements and different transition moment vectors involved in a two-state model approach. A close scrutiny of different parameters in 2SM clearly reveals that upon increasing the strength of either the donor or the acceptor group the parameters change in favour of increasing the overall δTP values but in the case of donors this effect is much larger. This journal is © the Owner Societies. Source

Coperet C.,CNRS Institute of Chemistry
Chemical Reviews | Year: 2010

A study was conducted to investigate C-H bond activation and organometallic intermediates on isolated metal centers on oxide surfaces. It was demonstrated that C-H bond activation was a ubiquitous process in heterogeneous catalysis that involved various types of mechanisms and intermediates. The study focused on investigating processes that involved C-H bond activation of alkenes and aromatics on isolated metal centers of surface oxide materials leading to organometallic species and intermediates. One potential pathway in alkene dehydrogenation involved the formation of a metal-alkyl intermediate that underwent β-H elimination and generated an alkene. It was demonstrated that cofeeding CO2 increased the activity and the stability of these nonoxidative dehydrogenation catalysts, as CO2 played the role of a mild oxidant and prevented coke formation. Source

Conley M.P.,ETH Zurich | Coperet C.,ETH Zurich | Thieuleux C.,CNRS Institute of Chemistry
ACS Catalysis | Year: 2014

Engineering heterogeneous catalysts with molecular precision is an ongoing challenge to access materials with predictable properties that can be optimized using quantitative structure-activity relationships. One approach is grafting organometallic complexes on dehydroxylated oxide supports using surface organometallic chemistry (SOMC). Although fruitful, this technique is limited to complexes containing a σ-bound surface oxygen in the first coordination sphere of the metal. In this perspective, we describe our recent efforts to incorporate molecular diversity onto surfaces to obtain molecularly defined heterogeneous catalysts containing N-heterocyclic carbene ligands for C-H activation, olefin metathesis, CO2 hydrogenation, and the Z-selective semihydrogenation of alkynes. © 2014 American Chemical Society. Source

Discover hidden collaborations