Computations on Fullerenes: Characterization, Reactivity and Growth

Identificador:  TDX:2683

Handle: https://hdl.handle.net/20.500.11797/TDX2683

Autores:  Abella Guzman, Laura

Resumen:
The Thesis titled ‘Computations on Fullerenes: Characterization, Reactivity and Growth’ is mainly focused on the formation mechanisms and characterization of fullerenes previously detected in experiments. These molecules are closed carbon cages formed by only hexagons and twelve pentagons. Most part of our research has been carried out in collaboration with different experimental groups, therefore we aimed to understand and rationalize their experiments. Although many hypothetical models have been proposed, the fullerene formation mechanism is still a mystery. Our studies rules out the bottom-up mechanism as a model of fullerene formation. We have explored this mechanism by means of static DFT and Car-Parrinello molecular dynamics calculations for series of different endohedral fullerenes. A comprehensive exploration of the most favourable isomers, potential energy surfaces associated with the successive C2 insertions and topologies of the involved structures, helped us to develop this project. The insertion of a C2 unit to already formed EMF is always an exothermic/exergonic process, and the free energy barriers for each step are attainable at temperature of fullerene formation (2000 K). The most abundant isomers of Ti@C2n (2n=26-48) and Sc3N@C2n (2n=68-80) are formally linked by direct C2 insertions and in a few cases by additional Stone-Wales transformations. Regarding the detection and isolation of endohedral metallofullerenes let us to perform a computational study of the rationalization and characterization of these isomers. Chlorination has emerged as a powerful tool in fullerene derivatives. Several C2n families (2n=50,60,66,68,etc.) have been found to show cages exohedrally chlorinated. According to our results, chlorination would take place at a temperature significantly lower than 2000 K by free radical addition considering the HOMO and the spin density distributions of the pristine cage and intermediates, once the lowest energy neutral isomers are formed. Most of our projects resulted in suitable and in agreement with experiments.