Unraveling interactions in large complex systems using quantum chemistry interpretative techniques and new generation polarizable force fields

In this contribution, following the results exposed at the Seventh International Conference of Computational Methods in Sciences and Engineering (ICCMSE 09), we present an overview of some available new techniques able to unravel interactions in large complex systems such as biomolecules, ions in solution, lanthanides and actinides complexes. We first focus our attention on Quantum Chemistry (QC) interpretative techniques introducing some Energy Decomposition Analysis (EDA) scheme such as the newly introduced fragment localized Single-CI DFT scheme. We then present the recently developed DEMEP analysis which is an extension of the topological analysis of the Electron Localization Function (ELF) to the computations of chemically intuitive local electrostatic moments. In a second part, we then discuss how such QC techniques can be used, following a "bottom-up" strategy in order to develop new generation polarizable force field based on distributed multipoles such as the AMOEBA and SIBFA (Sum of Interaction Between Fragments ab initio) procedure; or on electronic density as for the GEM (Gaussian electrostatic Model) method which is based on density fitting. Some applications are detailed.