Banca de QUALIFICAÇÃO: Alexandre Coelho Rodrigues Gomes

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : Alexandre Coelho Rodrigues Gomes
DATE: 26/02/2021
TIME: 10:00
LOCAL: campus 6
TITLE:

Computational prediction of the stability and decomposition
barriers of neutral molecular polynitrogens.

KEY WORDS:

Dft, polynitrogen, 

PAGES: 82
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Físico-Química
SPECIALTY: Química Teórica
SUMMARY:

This work presents a broad study on the stabilities of several neutral molecular polynitrogens
(polyN), with sizes six, eight and ten, focusing in theoretically predicting their usability as high-
energy-density materials (HEDMs). If stable enough to be synthesized and stored, these
systems may be used as a green source of energy. However, it is very difficult to obtain these
structures under mild experimental conditions. One of the main factors that can help this sort
of analysis is the predicition of the activation energy barriers of these structures towards
unimolecular decomposition. This latter was the basis of the discussions presented
throughtout the text. The calculation methodology applied for all the polyN was based on
density functional theory (DFT), using exchange and correlation functionals that are known for
their high accuracy in predicting energy barriers heights (M06-2X and SOGGA11-X). This
made possible a direct and fair comparison between all molecules analysed. The path taken
towards achieving this goal started with the search for transition states (TSs) that connected
the initial structures to unimolecular decomposition. After finding the TSs, an intrinsic reaction
coordinate calculation was carried out for each polyN in order to confirm the decomposition
mechanism found. For the most promising structures, a reaction dynamics study was made,
in order to check other possible decomposition routes. For this initial and exploratory part of
the work, the SOGGA11-X/def2-SVP level of theory was used. A refinement of the results
was then performed at the M06-2X,SOGGA11-X/def2-TZVPP levels, being the energies zero
pointed corrected. For a structural and electronic analysis of the systems, the average bond
lenghts, average bond orders, HOMO-LUMO gaps and asphericities were calculated. From
this analysis, it was possible to classify the structures in chains, rings, cages and prismatic
cages ones and achieve a correlation between the systems and their energy content.
However, it was not possible to assess a clear correlation between the activation energy
barriers of the structures with the calculated structural and electronic properties. The results
indicate that the prismatic caged polyN can be expected to present higher energy densities
and be more stable with respect to unimolecular decomposition. And finally, specific
structures could be selected as potential candidates for use as HEDMs.

BANKING MEMBERS:
Presidente - PATRICIA SANTIAGO DE OLIVEIRA PATRICIO
Externo à Instituição - LUÍS PEDRO VIEGAS - UC