Development and applications of quantum chemistry to open shell systems
Abstract
This thesis investigates the applicability of a range of computational techniques
across a range of open shell chemical systems from the geometrically simple but electronically complex to the geometrically complex but electronically simple. Initially
an investigation into a range of geometrically simple but electronically complicated
systems is presented. The Monte Carlo Configuration Interaction method (MCCI)
is applied to challenging transition metals dimers such as ScNi in order to establish
the ground state potential energy surface, from equilibrium bond lengths through to
dissociation using highly compact wavefunctions compared to Full Configuration Interaction (FCI). It shall be demonstrated that the ScNi dimer represents the current
limit of this technique. Software development of MCCI is then undertaken in order
to perform calculations of spin-orbit coupling interactions. Results on B, C, O, F, Si,
S, F, Cl, OH, NO, CN and C2 species are shown to be comparable with other techniques using the one-electron Breit-Pauli Hamiltonian. The application of quantum
chemistry to geometrically complex but electronically simple systems is then considered. Density Functional Theory (DFT) is used to investigate the mechanism and
energetic barriers leading to ring inversion of the biscalix[4]arene supra-molecule.
A minimum barrier height of 19.31 kcalmol−1 to inversion is elucidated along with
details of the complete mechanistic pathway to inversion. The focus then moves
to polymetallic clusters of calix[4]arene. A DFT study is made of the preferential
binding of calix[4]arene towards first row transition metals of various oxidation and spin states.
Results indicate that Cu3+ (singlet) species will preferentially bind to
the lower rim over other metals in the study. The final DFT-related work presented
is a study of the preferential binding at the upper rim of polymetallic calix[4]arene
clusters towards a range of important small gas molecules. It was found that gases
such as NH3 and SO2 bind most strongly to the upper rim with the inclusion of a
transition metal at the lower rim providing strengthening of the host-guest binding.