Theoretical calculations of the magnetic properties of inorganic molecules.

Abstract

The original research in this thesis is by Simon Jonathan Bennie for the degree of Doctor of Philosophy in 2013 in the subject of Theoretical Chemistry. The work was conducted at The University of Manchester in the School of Chemistry.The zero field splittings (ZFS) of inorganic molecules were studied with a view to understanding the applicability of new methods in Density Functional Theory (DFT). The initial thrust of this work was to benchmark the three methods available: Pederson Kahana, quasirestricted orbitals and the coupled perturbed equations. Simple 3d monometallic systems were studied with a unique focus on the effect of adjusting the basis set size of the metal. We also studied the effect of a range of commonly available functionals. We found that by using a large quadruple zeta basis set that the results of general gradient approximation (GGA) functionals can be improved. Hybrid functionals were found not to be as accurate as the GGAs and are often degraded by going to a larger basis. The degree of accuracy appears to be a function of the covalency of the metal to ligand bond as measured by the Mayer bond orders and Mulliken charges. We also present the results for complete active space self consistent field calculations and ZFS values for restricted open DFT determinants coupled with the multi-reference configuration interaction methods of obtaining the ZFS.Chapter 5 of this work focuses of the characterisation of a more complex di- chromium system called Kremer's dimer. This system has three magnetically active spin states each of which has well-defined ZFS values. Under the broken symmetry method we found no functional to be able to qualitatively reproduce the ordering of the spin state or the ZFS. Through analysis of the natural orbitals and spin eigenvalues we determined that this is due to a strong amount of multi-configurational character. Simple complete active space self consistent field (CASSCF) calculations were found to reproduce the experimental spin ladder. Multi-reference configuration interaction on the CASSCF solutions were found to accurately calculate the experimental ZFS values, with state optimised calculations being the most accurate choice for the CASSCF.

Date of Award	31 Dec 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Joseph J.W. Mcdouall (Supervisor)