Chemistry PhD Final Defense – Brooke Bonar

About the event

Speaker: Brooke Bonar

Group: Dr. Kirk Peterson

Title: ACCURATE AB INITIO THERMOCHEMISTRY USING FULLY RELATIVISTIC APPROACHES

Abstract:

This work employs spinor- and scalar-based fully relativistic coupled cluster composite approaches to calculate accurate thermochemical properties of molecules, with a particular focus on heavy element systems, and an expected accuracy of 3 kcal/mol throughout. Broadly, the composite thermochemistry methods based on the Feller-Peterson-Dixon (FPD) approach have been utilized with differences in the treatment of spin-orbit coupling. The spinor-based relativistic CCSD(T) calculations include spin-orbit at the orbital level while the scalar-based relativistic CCSD(T) incorporates a posteriori SO contributions based on 2-component multireference configuration interaction calculations. The bond dissociation energies (BDEs) of AnX0/+ and the ionization energies (IEs) of AnX (An=Ac-Lr and X=F-I) molecules are presented. For most of these molecules, the BDEs and IEs presented in this work are the first in the literature. FPD BDEs for the fluorides were used to confirm the trend across the actinide series previously predicted by Gibson using bonding models based atomic promotion energies that provide a single 6d electron for bonding. In particular the local minimum in the BDEs at AmF0/+ is confirmed in the present calculations. A similar spinor-based FPD approach was also employed to calculate the BDEs of RgF and CnF0/+, as well as the IE of CnF. These results were then compared to their transition metal congeners, AuF and HgF0/+, respectively. Finally, this dissertation tackles two methodological questions. The first directly compares scalar-based results of XO0/- (X=Cl, Br, I) to spinor-based results. This comparison concluded both approaches yield miraculously similar contributions. Finally, this dissertation investigates auxiliary field quantum Monte Carlo, an approach which allows for multideterminantal wavefunctions, for use within an FPD composite approach.