Multiscale modeling of chemical systems in solution by coupling multiconfigurational approaches to the fluctuating charges polarizable force field

The investigation of electronic transitions in solution is a useful tool to gather information on systems involved in important chemical or biological processes that occurs in liquid phase. Therefore, from a computational point of view, a reasonable way to address this is to resort to multiscale modeling [1]. Among these methods, hybrid approaches based on the coupling between a quantum mechanical method and the Fluctuacting charges (FQ) polarizable force field [2,3] are presented. Many interesting solvated systems comprise solutes with complex electronic structures, e.g. conjugated systems, chromophores in photosensitive proteins or transition metal enzymes. These complex electronic structures need to be described by an accurate multiconfigurational QM approach. In this talk I will introduce the methodological foundation of the FQ coupling with (stochastic) multiconfigurational and perturbation theory strategies, namely, CASSCF/FQ [4], DMRG/FQ [5], as well as FCIQMC [6], Stochastic-CASSCF [7] and the recent Stochastic-SplitGAS [8]. Application of these QM/FQ strategies are presented, in the form of simulations of vertical excitation energies and solvatochromic shifts of a set of molecules in solution.

References:
[1] A. Warshel, M. Levitt, J. Mol. Biol. 103 (1976) 227
[2] S. W. Rick, S. J. Stuart, B.J. Berne, J. Chem. Phys. 101 (1994) 6141
[3] T. Giovannini, F. Egidi, C. Cappelli, Chem. Soc. Rev. 49 (2020) 5664
[4] C. Sepali, L. Goletto, P. Lafiosca, M. Rinaldi, T. Giovannini, C. Cappelli, J. Chem. Theory Comput. 20 (2024) 9954
[5] M. Rinaldi, C. Sepali, A.M. Kirk, C. Amovilli, C. Cappelli in preparation
[6] G. H. Booth, A. J. W. Thom, A. Alavi, J. Chem. Phys. 131 (2009) 054106
[7] G. Li Manni, S. D. Smart, A. Alavi, J. Chem. Theory Comput. 12 (2016) 1245
[8] L. Bonfirraro, O. Weser, M. Song, G. Li Manni, ChemRxiv (2025)