The role of static and dynamic correlation in molecular electronic structure, spectroscopy, and intermolecular interactions.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Electron correlation is a central problem in quantum chemistry. This thesis explores the role that static and dynamic correlation play in three different computational applications: The basis set dependence of energy calculations; the formation of a dicationic dimer; and the calculation of the spectra and ground states of metallophthalocyanines. The basis set dependence of the static correlation energy is established for a chemically diverse collection of atoms and molecules, and shown to converge exponentially with respect to basis set cardinality. For most practical purposes, a triple zeta basis set is sufficient to recover the static correlation energy with high accuracy. A new dicationic dimer system comprised of closed shell monomers is examined, to determine what forces are driving dimer formation. It is demonstrated that dynamic correlation energy overcomes the electrostatic repulsion between the cations, when supplemented by charge-‐balancing environmental effects, and therefore lead to dimer formation. Explaining the electronic spectra of the metallophthalocyanine molecules has posed a problem for spectroscopists for over 30 years. Static correlation is found to play a determining role in excited state energies due to the presence of a number of energetically-‐close π-‐orbitals. The experimental spectrum of zinc phthalocyanine is reproduced computationally with EOM-‐CCSD based methods giving the experimentally observed number of peaks all within 0.4 eV of observed experimental energies. Past DFT studies on the ground states of the Mn, Fe, and Co phthalocyanines have disagreed concerning the ground state orbital occupations of the metal ions for these systems. This thesis uses CASSCF-‐based methods to predict the ground states of these systems, which are determined to be Mn: (dxy)2(dxz,dyz)1,1(dz2)1, Co: (dxy)2(dxz,dyz)2,2(dz2)1. For Fe two possibilities for the ground state were found to be within 0.02 eV of each other in the highest-‐quality calculations: (dxy)2(dxz,dyz)1,1(dz2)2 and (dxy)2(dxz,dyz)2,1(dz2)1.