Background:
Summary of Methods Used
Simple Example:
Theory
The Vibrations
Research Topics:
Fatty Acid Methyl Esters (FAMEs)
School of Chemistry
The Queen's University of Belfast
Non-Planar Porphyrins
It was essential that we validated our computational method using a smaller system, and porphine was ideal for this purpose. The Raman spectra of this molecule have been studied for many years, so it’s a very well understood system.
In addition to the wealth of experimental work, many calculations have been carried out at a high level of theory in conjunction with large basis sets and when we carried out our own calculations using scaled 6-31G(d) frequencies we found that they were in good agreement with these other calculations.
So we were confident that our method would be sufficiently good to allow meaningful calculations to be carried out on TtBP, but we had to ensure that the molecule had the correct symmetry so that the symmetry labels of each vibrational mode would be included in the output – I’ll explain why this was important on the next page.
However, needless to say – trying to obtain calculations with the correct symmetry on such a floppy molecule was quite difficult and what we ended up doing was to start with just the porphine core in a ruffled geometry and then we added on substituents little by little until we had built up the whole molecule to have D2 symmetry. But – it’s a good job that we were able to manage that, because even with the D2 symmetry it still took around 35 days to complete the geometry optimisation and frequency calculation.
