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On the importance and challenges of modelling extraterrestrial photopigments via density-functional theory

Presentation #223.11 in the session Exoplanet Atmospheres (Poster + Lightning Talk)

Published onOct 23, 2023
On the importance and challenges of modelling extraterrestrial photopigments via density-functional theory

Photosynthesis is a cornerstone of life on Earth, occurring in both terrestrial and aquatic ecosystems. Oxygenic photosynthesis, which produces molecular oxygen, dominates in terms of biomass, and understanding it is crucial due to its biological and potential renewable energy applications. Furthermore, its significance extends to astrobiology, particularly in the study of exoplanets. Investigating photosynthesis in this context may help answer the fundamental question of extraterrestrial life. The detection of photosynthesis on other planets raises the question of how it can be identified using advanced telescopes. In this context, two major biological signatures should be introduced. One of them being molecular oxygen (O2) and the other one known as the Vegetation Red Edge (VRE). While O2 can have false positives, the VRE is a robust biosignature since it has no known false positives, and photopigments are canonically perceived as reliable signatures of extraterrestrial life. The VRE shows that the absorbance of most Chls declines beyond the Qy absorption band at 650-700 nm. However, it is not guaranteed that extraterrestrial photopigments would be identical to chlorophylls (Chls), which is the reason for this research project. We focused on exploring modifications of naturally occurring photopigments, like Chlorophyll a (Chl a) and its precursor Phot0. To do so we used and compared various DFT functionals to modell UV/Vis absorption spectra. In this process, we found that modern range-separated hybrid functionals show the highest agreement with high-level calculations and experiments. Therefore, we suggest that users should avoid local and low-exchange functionals and should opt for using such range-separated functionals.

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