Carregant...
Tipus de document
TesiVersió
Versió publicadaData de publicació
Llicència de publicació
Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/123346
Quantum Confinement of Gaseous Molecules in Nanostructures: Effects on the Dynamics and Internal Structure
Títol de la revista
Autors
Director/Tutor
ISSN de la revista
Títol del volum
Recurs relacionat
Resum
[eng] Quantum confinement effects, understood as the changes on the structure and dynamics of a molecule when it goes from a free environment to a cavity with some characteristic length of the order of the nanometer, represent both a challenge and an opportunity. A challenge, because there is still work to be done in order to be able to understand and model them properly. An opportunity, because they offer the means to tune molecular properties such as adsorption, diffusion, or even reactivity.
The present Doctoral Thesis is focused on the theoretical and computational study of the system consisting on a single H2 (or D2) molecule trapped in the hollow cavity of a narrow Single--walled Carbon Nanotube. Since Dillon and coworkers suggested in 1997 the existence of quantum confinement effects as an explanation for the unexpectedly high H2 uptake in carbon nanotubes, this particular system has received much attention from theoretical and experimental points of view. Here we intend to gain more insight on it by developing new analysis tools for high dimensional eigenstates, and by improving the model with respect to previous works. The former has been achieved through the use of overlap and partial overlap functions, which has provided with an intuitive way to understand the coupling between the different degrees of freedom by comparison of the actual eigenstates of the system with a separable model. Regarding the improvement of the model, we have worked on it from two perspectives: first, we have included new molecular degrees of freedom to the system, namely the motion of the center of mass of the molecule along the axis of the nanotube. This has allowed us to obtain diffusion rates for H2 and D2 inside the nanotube in a full quantum mechanics framework, which to the best of our knowledge had not been achieved before. The study of the diffusion dynamics has also allowed us to define an adiabatic representation of the Hamiltonian, taking advantage of the quasi separability of the diffusion coordinate and the remaining degrees of freedom, to increase the efficiency of the propagations with high accuracy. As a second means to improve the model, we have developed a system--bath coupling Hamiltonian in order to see how the phonons of the nanostructure affect the dynamics of the confined molecule. We have seen that both sets of degrees of freedom (molecular and phonons) are strongly coupled due to the linear momentum exchange between them. Time--dependent Perturbation Theory calculations have determined that the characteristic time for the momentum exchange is shorter than that for diffusion, which suggests that the friction with the nanotube may have a relevant effect on the transport properties of the confined molecule.
Matèries
Matèries (anglès)
Citació
Citació
MONDELO-MARTELL, Manel. Quantum Confinement of Gaseous Molecules in Nanostructures: Effects on the Dynamics and Internal Structure. [consulta: 14 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/123346]