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Vincent ROBERT - Research interests

Paramagnetic NMR for Large systems Cu3

The purpose of wavefunction-based calculations is to elucidate the mechanisms at the origin of unusual low-energy spectroscopies. Not only accurate energy differences can be reached but the reading of the wavefunction is also very insightful in the properties growing. Multireference approaches working with the exact Hamiltonian (CASSCF + dynamical correlation effects) are currently performed on various dimensionality systems. Much efforts are currently dedicated to the use of orbitals localization techniques which allow one to handle much larger systems with ab initio approaches.

Antiferromagnetic behavior based on quasi-orthogonal MOs: an ab initio analysis of a synthetic trinuclear Cu3 oxidase model Download
Le Guennic, B.; Petit, S.; Chastanet, G.; Pilet, G.; Luneau, D.; Ben Amor, N.; Robert, V.
Inorganic Chemistry 2008, 47, 572-577.


Paramagnetic NMR spectra simulation for crystal structures

In the presence of paramagnetic centers (e.g. V(IV) ion) in the crystal structures, NMR spectra are greatly affected and temperature-dependent. Ab initio calculations give access to magnetic exchange patterns which govern the electronic spin density. The paramagnetic NMR spectra simulation can be used to probe the crystal structures in such materials.

Exchange Interactions in the Three Phases of the Vanadyl Pyrophosphate (VO)2P2O7 Download
Petit, S.; Borshch, S.; Robert, V.
Journal of the American Chemical Society 2002, 124, 1744-1747.


Spin Transition - Hysteretic Behavior

The constant facination for spin transiting systems arises from their anticipated applications as potential magnetic memory devices . Our main interest is to evaluate accurate adiabatic energy difference to rationalize the factors which may govern the transition and identify the subtle interplay between the so-called weak bonds which are determinant in growing hysteresis loops.

The analysis of the Low-Spin and High-Spin wavefunctions of the transiting units gives access to important information regarding the electronic distribution. Taking advantage of such ab initio information, thermodynamics models are currently being developed to give some new insights in the hysteretic behavior.

Energetics of [Fe(NCH)6]2+ via CASPT2 calculations: a spin-crossover perspective Download
Kepenekian, M.; Le Guennic, B.; de Graaf, C.; Robert, V.
Journal of Computational Chemistry 2009, 30, 2327-2333.

Prussian Blue Analogue CsFe[Cr(CN)6] as a Matrix for the Fe(II) Download
Spin-Crossover Le Guennic, B. ; Borshch, S. A. ; Robert, V.
Inorganic Chemistry, 2007, 46, 11106-11111.

Magnetic Bistability: from Microscopic to Macroscopic Understandings of Hysteretic Behavior using ab initio Calculations Download
Kepenekian, M.; Le Guennic, B.; Robert, V.
Physical Review B 2009, 79, 094428.


Noninnocent ligands - Porphyrins bistability

The so-called noninnocent class of ligands (e.g. verdazyl, thiazyl, glyoxalmercapto) has considerably enlarged the potentiality of metal ion complexes since both the metal and ligands are likely to participate in the magnetic properties. Both partners should be treated on the same footing and it has been suggested that an explicitely correlated inspection is required. Rather unusual behavior and spin states have been identified. A spin-transition like transition phenomenon and an original metal field theory have been suggested.

Very promising behavior are expected (e.g. ferromagnetism, bistability) when biological targets are used. The low-energy spectroscopy of non-heme synthetic systems exhibit spin-transiting-like behavior.

Ab Initio Study of Intriguing Coordination Complexes : A Metal Field Theory Picture Download
Guihéry, N.; Robert, V.; Neese, F.
Journal of Physical Chemistry A 2008, 112, 12975-12979.

Inspection of the Duality of a Verdazyl-Based Radical in Transition Metal Complexes: A π* Donor Ligand and a Magnetic Download
Partner Rota, J.B.; Norel, L.; Train, C.; Ben Amor, N.; Maynau, D.; Robert, V.
Journal of the American Chemical Society 2008, 130, 10380-10385.


Multifunctionnality : Magnetic properties and Non-Linear Optics

The rapid development of sophisticated objects has motivated the preparation of specific targets holding various properties. The simultaneous presence of different properties and their non-independent control has become a real challenge in materials preparation. Specific Non-Linear-Optic active organic systems (catechol-based) can be prepared to enventually bind some specific ion center to generate tunable magneto-optical systems.

The inclusion of rare-earth elements is likely to introduce some specific electronic effects (high spin, anisotropy) and unusual magnetic behavior along with specific optical properties. An original approach based upon wavefunction calculations is currently being developed to evaluate the hyperpolarizabilities of targets molecules. The relevance of charge transfer states is analyzed in the determination of NLO properties.

A Rational Design of Catechol-based Compounds: Experimental and Theoretical study of Optical Properties Download
Aronica, C.; Venancio-Marques, A.; Chauvin, J.; Robert, V.; Lemercier, G.
Chemistry- A European Journal 2009, 15, 5047-5055.


Electron transfer : Vibronic Interactions and Valence Tautomerism

A new class of molecular complexes based upon Co ion and electrocative ligands has considerably opened the field of bistability. The simultaneous changes in the electronic distribution and spin states is accompanied by metal-ligand bond distances modifications. Such valence tautomerism is being analyzed on the basis of wavefunction calculations to shed light in the spin states and the electron transfer phenomenon.

In the mean time, phenomenological models of vibronic origin are developed to evaluate the different regimes in quasi monodimensional systems. The importance of electron-phonon coupling is known to play a major role in the transport properties of quasi-1D systems.

A Vibronic Approach to the Band-Filling and Temperature-Dependent Metal-Insulator Transition Download
Robert, V.
Journal of Chemical Physics 2004, 121, 4297-4301.


Extended Systems : Parametrization and Methodological approaches

Even though the electronic inspection of delocalized systems traditionnaly relies on Bloch's theorem, an original self-consistent coupled-cluster method has demonstrated that the energetics can be accurately evaluated using a localized picture. The method allows for a splitting of the different energy contributions, and the definition and competition of aromatic vs. non-aromatic effects in 2D architectures.

Since the strategy based on a rational construction of the wavefunction turns out to be successful for the ground state characterization, promising strategies are considered to characterize the excited states of extended systems. Such methodology is to be compared with standard physical theory-based methods to evaluate the charge band gaps of systems ruled by Huckel and Hubbard Hamiltonians.

Evaluation of the aromatic contribution to the energy of periodic lattices Download
Malrieu, J.-P.; Robert, V.
Journal of Physical Organic Chemistry 2006, 19 (1), 10-17.


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