Probing Mn-Mn and Mn-Si bonding in silicon cages

This thesis explores the geometry and electronic structure of some manganese doped silicon clusters. Experimental characterisation of these clusters is severely limited. Theoretical investigations with density functional theory (DFT) yield conflicting results due to differences in the choice of functional. Hence, a combination of both theory and experiment has been employed: our experimental collaborators have measured the IR-MPD spectra of these clusters while we have used DFT calculations to explore the potential energy surfaces. For a given cluster, the vibrational spectra for low-lying isomers have been computed and compared with the measured spectrum to identify the experimentally observed isomers. The information content of the spectra has been expanded by assigning vibrational modes to various peaks and by identifying vibrational signatures. Given that there is no consensus about the choice of functional, the results have been computed with a range of functionals. The influence of functional choice on the conclusions has been studied which reveals how certain functionals stabilise structures with low vertex connectivity while others tend to favour deltahedral frameworks. Multiconfigurational self-consistent field theory (MC-SCF) has been used to get an alternative perspective on bonding in these clusters. By making use of generalised and restricted active spaces (GAS and RAS), important contributions to static correlation in these clusters have been probed. An attempt has been made to account for dynamic correlation by applying perturbation theory corrections to energies obtained by the RASSCF method. However, sufficient static correlation has not been captured in the RASSCF wavefunction to allow for a reliable perturbative treatment of the remaining, missing, correlation