Multiscale QM/classical models based on the GW approximation coupled with the Fluctuating Charges force field

This thesis discusses a multiscale model that integrates the GW approximation with fluctuating charges (FQ) and fluctuating charges and dipoles force fields (FQFµ) to improve the chemical description of molecular systems in solution. The work addresses two main challenges in theoretical chemistry: the accurate evaluation of electronic correlation and the inclusion of solvation effects. The GW approximation is a field theory method useful for calculating the electronic structure of molecules, employing Green's function to represent many-body systems. Methods like FQ and FQFµ simulate environmental effects through electrostatic interactions, modeling the solvent as a distribution of electric multipoles. The aim of this work is to combine these approaches to improve the description of molecular properties in solution, with particular attention to ionization potentials. The numerical part of the work focuses on simulations of three molecular compounds in aqueous solution: adenine, the chromophore of green fluorescent protein, and cytosine. Results obtained employing different methods are compared, including calculations in vacuo, continuum solvation methods and the Discrete Reaction Field (DRF) approach.