My first taste of quantum chemistry research involved generating simpler Gaussian representations for the shell-pairs in Q-Chem. As the calculation of electron integrals, which use the shell-pair data, is the rate-limiting step for the majority of modern calculations, any simplification in the shell-pair data will give a significant speed-up in the total time taken for the calculation. This work culminated in my B.Sc(Hons). report to Massey University in 1994.
I then began my first collaboration with Prof. John Pople (the 1998 Chemistry Nobel Prize winner!), investigating partitioning the electron density. The effect of these partitions on the behaviour of density functionals was then examined.
Most of my researching time has been spent on the next topic I investigated, the CASE approximation. This formed the majority of my Ph.D. thesis last year. Nuclei and electrons interact with each other via the Coulomb operator, which decays very slowly. Because of this interactions between particles that are very far apart still have to be calculated, even though we can expect there to be little or no effect from atoms at the other side of a large molecule. The CASE approximation attenuates the Coulomb operator so that distant particles don't interact (hence their interaction does not need to be calculated). The trick is to attenuate the operator in such a way that the interactions of near particles is not destroyed.
During this time I have also investigated, in collaboration with Dr Terry Adams, faster ways to calculate electron-electron integrals (wether attenuated or not), forming part of the COLD prism which has been implemented in the Q-Chem program.
My last branch of research has been a continuation of the collaboration with Prof. Pople, looking for new density functionals. We have used the G2 data set to try and introduce a completely empirical functional with as few parameters as possible (while retaining useful accuracy). This has resulted in the empirical density functional EDF1, specfically designed for a small basis set.
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