Optical Excitations of Chlorophyll <i>a</i> and Chlorophyll <i>b</i> Monomers and Dimers

Journal Of Chemical Theory And Computation (submitted), (2017)

Optical Excitations of Chlorophyll a and Chlorophyll b Monomers and Dimers

María Rosa Preciado-Rivas, Duncan John Mowbray, Ask Hjorth Larsen, Bruce Forbes Milne

A necessary first step in the development of technologies such as artificial photosynthesis is understanding the photoexcitation process within the basic building blocks of naturally-occuring light harvesting complexes (LHCs). The most important of these building blocks in biological LHCs such as LHC II from green plants are the chlorophyll a (Chla) and chlorophyll b (Chl b) chromophores dispersed throughout the protein matrix. Efforts are still hampered by the lack of economical computational methods that are able to describe optical absorption in large biomolecules with sufficient accuracy. In this work we employ a highly efficient localized basis set representation of the Kohn--Sham (KS) wave functions at the density functional theory (DFT) level to perform time dependent density functional theory (TDDFT) real time and frequency domain calculations of the optical absorption spectra of Chl a and Chl b monomers and dimers. We find our TDDFT calculations using linear combinations of atomic orbitals (LCAO) reproduce results obtained with a plane wave (PW) and real space (RS) representations of the KS wave functions, but with a significant reduction in computational effort. This work opens the path to first principles calculations of optical excitations in macromolecular systems.

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