

Methods and theoretical tools for biological systems 
Valérie Brenner 
The theoretical activities are focussed onto the modelling of large molecular systems using quantum chemistry methods, which is a theoretical challenge for these methods. These modeeling actions are either connected to the gas phase experimental investigations carried out in the group, or are done in support of nuclear activities of the applied programs of CEA. Recent developments in quantum chemistry methods are thus used to implement strategies of calculations and / or theoretical models to obtain a better understanding of these complex systems. The systems of biological interest are very flexible systems, mediumsized (10100 atoms) systems, whose structure is controlled by noncovalent interactions and whose excited states can exhibit very different natures (e.g., locally excited states, chargetransfer states, etc...). 
Modelling their ground state conformational landscape is based on a multistep theoretical strategy, leading in fine to a confrontation with the experimental data:
The excited state modelling includes two actions:
These studies are focussed onto the interaction or rare gases with open shell atoms in small model systems containing small molecules, and will be extended to more realistic models, namely small SiC clusters, representing one or two solvation shells of a rare gas atom; SiC being a typical material of interest for nuclear industry (Coll. CEA  DEN/DEC/SESC/LCC et Projet Fédérateur NEEDS FPMatériaux). These DFT calculations are systematically validated by comparison with the more accurate quantum chemistry method, i.e., Coupled Cluster at the CCSD(T) level. 