During my Ph.D. I have been lucky enough to work in two universities, with very different departments, meeting a great deal of people who have helped me in my research. Throughout this time I have been extremely fortunate to have a supervisor of the calibre of Dr Peter Gill. For his constant encouragement, scientific guidance and friendship I am very grateful. I would also like to thank the patient supervision afforded to me by Professor John Pople, whose periodic visits proved very productive.
Help and comradeship from members of the ``sweatbox'' at Massey were invaluable, especially Dr Jeremy Dombroski's assistance with system administration and Dr Terry Adams' (not forgetting Gwen and Emily's) unending support, including short-notice accommodation in Pittsburgh.
I also owe a debt of thanks to the members of the Q-CHEM group at Cambridge: Aaron, Katrina, Oliver, Andrew, Nikhil and Simon have all in some way contributed to this thesis. Prosit!
To all the gang at Trinity, particularly my three flatmates, who have all helped make my time at Cambridge an enjoyable one, I am most grateful. A special thank you to Sharon, who has not only helped immensely with proofreading, but has had to put up with the stress and bad moods associated with completing a Ph.D.
Finally, I would like to acknowledge the financial support from Massey University , the ORS awards scheme, the Cambridge Commonwealth Trust and Trinity College.