Development of Density Functional Methods for Electronic Excited States and the Influence of Molecular Structure on Electronic Excited States

Fletcher, Peter and Peach, Michael (2021) Development of Density Functional Methods for Electronic Excited States and the Influence of Molecular Structure on Electronic Excited States. PhD thesis, Lancaster University.

Text (2021PeterFletcherPhD)
2021PeterFletcherphd.pdf - Published Version
Available under License Creative Commons Attribution-NonCommercial-NoDerivs.
Download (4MB)

Abstract

An extensive assessment of six density functional approximations has been undertaken, each of these approximations have their own merits and faults. Range separated hybrids are the best performing for excited state properties of those approximations assessed. There has been an attempt to generate an attenuated form of PBE (CAM-PBE) which initially had issues which were investigated in detail regarding the dependence of Hartree–Fock exchange energy on approximation performance. This attenuated form of PBE had similar performance to CAM-B3LYP. The development of a set of benchmark data for excited state geometries and emission energies was undertaken with a wide range of organic molecules due to the lack of such benchmark data existing currently. This means the accuracy of density functional approximations for calculation of such properties is unknown so there is a clear need for this benchmark data to be developed and used to assess the accuracy of these approximations. The benchmark data for excited state geometries and emission energies was used to assess the performance of a range of density functional approximations for these properties. This assessment has suggested that there are issues when applying current density functional approximations away from the ground state where they have been tuned and optimised. This suggests that there may be some merit in developing specialised density functional approximations for the calculation of excited state properties. The existing density functional approximations have been used to assist with experimental investigations of porous polymers and in explaining the excited state properties of these polymers. This was done using model systems and has enabled a deeper understanding of the experimental observations