Ab initio parametrization of a generalized Hubbard model in a molecule displaying chirality-induced spin selectivity

Chirality-induced spin selectivity (CISS) refers to the interplay between molecule handedness and the electron spin. Despite ample experimental evidence, the mechanism leading to CISS is not fully understood yet. In this work, we present an ab initio study of a chiral molecule that exhibits CISS upon photoinduced electron transfer. Using DFT and TD-DFT we obtain good agreement with experimental absorption spectra, revealing weak electronic coupling between donor, chiral bridge, and acceptor. To accurately capture electronic correlations, we develop a novel approach to derive a multi-orbital Hubbard model describing the chiral bridge, where all parameters are obtained from ab initio CASCI calculations. This offers a versatile framework that can be extended to other molecular systems. Beyond electronic effects, we explore the role of low-energy vibrations, assessing their impact on the inter-site Hubbard parameters and simulating the system’s time evolution via unitary dynamics. Our results indicate that electron-vibration coupling leads to a non-negligible spin polarization, highlighting its potential relevance in the CISS mechanism.