Development and Implementation of Methods in Theoretical Chemistry

Abstract: The method development research in the field of theoretical chemistry is the never ending quest for methods that are faster, gives more accurate results, and expands the possibilities. The work in this thesis is no exception to that statement. Thus a CI routine more suited for calculations on large active spaces was implemented in the RASSCF code of Molcas; a new scheme for localizing multipole moments and polarizabilities were developed and implemented; and a parallel SCF code that provides super linear speed up saw the light of the day. These implementations were largely used throughout the remainder of the work, where the nuclear quadrupole moment of tin and the electronic spectrum of UO2 were determined; the photodissociation of bromoiodomethane was investigated; and the ability of localized properties to reproduce the electrostatic potential was tested.