Generation of molecular systems of astrophysical and technological interesta theoretical study of the first steps in the chemistry of microhydrated al systems

Resumo

The main objective of this Thesis is to shed some light on the reactivity of Aluminum (individual atoms and small/medium-sized clusters) with water, which is an important reaction from an astrophysical, chemical and technological point of view. We have been working on the reactivity of Al (atom and clusters) with water both energetic and dynamically (note that one of the principal aims is to clarify the importance of water catalysis by relay mechanisms). With that purpose, we have employed several theoretical techniques: - Electronic Structure Methods * High-level ab initio techniques (for the description of the smallest systems), which include relativity, core correlations, basis set extrapolations, or alternatively, the use of F12-based Coupled-Cluster methods. * Excited state calculations: We have employed the multi-configuration SCF method (MCSCF) and the multi-reference CI methods (MRCI). * An "onion-type" methodology, that we can summarized as DFT/EFP/PCM, for dealing with an individual atom surrounded by many hydration water molecules. * DFT methods: We have studied the coalescence of hydrated AlOH molecules and the microhydrated Al clusters by means of DFT. - Reaction Dynamics Methods * Transition State Theory (TST), in its canonical (T-dependent) or micro-canonical (E-dependent) forms, taking tunneling into account by means of unsymmetrical Eckart barrier as wells as other more developed methods (SCT, LCT ...). These more developed tunneling methods were applied in the smallest system, i.e. for the Al-H2O interaction. * The Instanton method: It was useful to understand more deeply the tunneling effect in the Grotthuss-like (or relay type) mechanisms observed in the multihydrated systems. * Molecular Dynamics of the sometimes called "Born-Oppenheimer" type (i.e. semi-classical simulations). a) DFT trajectories on a particular electronic state; typically as a way to monitor energy flows and find alternative local minima. b) Non-adiabatic dynamics, with the fewest-switches algorithm to deal with photoemission effects.