| Summary: | Quantum mechanical methods are becoming increasingly useful and applicable tools to
complement and support experiment. Nonetheless, some barriers to further
applications of theoretical models still remain. A coupled cluster singles and
doubles (CCSD) calculation, a reliable textit{ab initio} method, scales
approximately on the order of ${cal O}(N^6)$, where $N$ is a measure of the system
size. This unfortunately limits the use of such high-accuracy methods to
relatively small systems.
Coupled cluster property calculations must be used in conjunction with
reduced-scaling methods in order to broaden the range of applications to larger
systems. In this work, we introduce some of the underlying theory behind such
calculations and test the performance of several local correlation techniques
for polarizabilities, optical rotations, and excited state properties. In
general, when the computational cost is significantly reduced, the necessary
accuracy is lost. Polarizabilities are less sensitive to the truncation
schemes than optical rotations, and the excitation data is often only in
agreement with the canonical result for the first few excited states.
Additionally, we present a novel application of equation-of-motion coupled
cluster singles and doubles to simulated circularly polarized luminescence
spectra of eight chiral ketones. Both the absorption in the ground state and
emission from the excited states were examined. Extensive geometry analyses
were performed, revealing that optimized structures at the density functional
theory were adequate for the calculation accurate coupled cluster excitation
data. === Ph. D.
|
|---|
