Revealing the chemical bonding and the reorganization of the chemical bonds forms the undisputed foundation of chemistry. However theoretical chemists are limited by the fact that bonds are not univocally defined, nor easy to quantify. The Chemical Interpretation team at the LCT works in the development of the interpretative models that are necessary to recover chemical structure and reactivity, and more specifically to understand the process of bond formation and breaking during reactions.
- Chemistry in Hilbert Space
Molecular Orbital (MO) theory has been very useful and successful for the theoretical analysis of chemical reactions and chemical reactivity. Important connections with the energy of the system are currently under study in terms of derivatives of MO energies (Dynamic Orbital Force, DOF). Whereas MOs can extend over the entire molecule, Valence Bond (VB) theory by using localized non-orthogonal orbitals concentrates on the idea that that electron pairs are essentially located between two specific atoms in a molecule, which enables to retrieve directly from VB wave functions familiar chemical concepts such as Lewis structures, resonance / mesomery, hybridization, etc. Our efforts are currently focused on extended VB to metallic systems and excited states.
2. Quantum Chemical Topology
In a deliberate wish to simplify the dimensionality of the Hilbert space problem, 3D interpretative approaches have been introduced, such as the topological approaches. Within the topological approach, the 3D space is divided into mutually disjoint regions following the gradient of a scalar function. Important efforts are done in the development and application of the Quantum Theory of Atoms In Molecules (QTAIM) and the Electron Localization Function (ELF). However, also original approaches, such as Maximum Probability Domains (MPDs), which enable to recover the regions of space where the probability of finding N electrons is maximal, are also a fruitful line of research.
Codes: ELF : Topmod, Topchem, Topol, MPDs
3. Approaches for weak Interactions
Non covalent interactions might become even more crucial when talking about reactivity, stability of big systems or catalysis. Hence we also work intensely on tools for revealing non-covalent interactions in real space, such as the Non Covalent Interaction (NCI) index. Our current efforts are directed at the quantification of NCI regions and the relationship with the energy.
J. CONTRERAS-GARCIA (Chef d’équipe )