## Theory Project: Implementation of an effective method to simulate optical spectra

The calculation of Franck-Condon factors (FCF) is crucial for simulating optical spectra (OS) of molecules and calculating the rate constants of electronic transitions using Fermi's golden rule. While the number of FCF is, in principle, infinite, most of them are almost zero. This means that spectra can be well converged by using a limited number of FCF. However, the number of non-zero FCF increases rapidly with the number of the available vibrational states, making the computation of OS specially challenging for large molecules.

The goal of this project is to implement a systematic methodology to determine a minimal set of FCF that can be used to compute optical spectra to an arbitrary level of accuracy. This implementation will be done on a pre-existing code: PyQchem; a python interface for Q-Chem designed to automize complex computational chemistry calculations.

The candidate should have good knowledge of quantum mechanics and electronic structure theory of molecules (assumed in chemistry and physics BSc. students) and advanced level skills on scientific coding (languages: Fortran, C, C++, Python...).

**Supervisor:** David Casanova and Abel Carreras

Molecular Electronic Structure Group

Donostia International Physics Center, Donostia-San Sebastian