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Ab initio calculation of UV-absorption spectra of chlorophyll a: Comparison study between RHF/CIS, TDDFT, and semi-empirical methods
Veinardi Suendo1,3,* & Sparisoma Viridi2
1Inorganic and Physical Chemistry Research Division, Department of Chemistry, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung,
Jalan Ganesha 10, Bandung 40132, Jawa Barat, Indonesia
2Nuclear Physics and Biophysics Research Division, Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung,
Jalan Ganesha 10, Bandung 40132, Jawa Barat, Indonesia
3National Center for Nanotechnology, Jalan Ganesha 10, Bandung 40132,
Jawa Barat, Indonesia
Email : vsuendo@chem.itb.ac.id
Abstract. Chlorophyll a is one the most abundant pigment on Earth that responsible for trapping the light energy to perform photosynthesis in green plants. This molecule has been studied for many years from different point of views in both experimental and theoretical interests. In this study, the restricted Hartree-Fock configuration interaction single (RHF/CIS), time-dependent density functional theory (TDDFT) and several semi-empirical methods (CNDO/s and ZINDO) calculations were carried out to reconstruct the UV-Vis absorption spectra of chlorophyll a. In some extend, the calculation results based on single molecule approach were succeeded to reconstruct the absorption spectra but required to be rescaled to fit the experimental one. In general, the semi-empirical methods provide better energy scaling factor that closer to unity. However, they lack of vertical transition fine features with respect to the spectrum obtained experimentally. Here, the ab initio calculations provide more complete features, especially the TDDFT at high level of basis sets that also has a good accuracy in the transition energies. The contribution of ground states and excited states orbitals in the main vertical transitions is discussed based on delocalization nature of the wavefunctions and the presence of solvent through polarizable continuum model (PCM).
Keywords: Chlorophyll a; CIS; CNDO/S; Electronic transition; TDDFT; UV-Vis
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