| Cis-trans photoisomerization is a chemical reaction which converts light to mechanical energy on a molecular scale. Unique methods which provide an accurate theoretical description of these reactions are presented here. An implementation of the ab initio multiple spawning (AIMS) dynamics algorithm has been developed to simulate photodynamics. This method can simulate the full time-dependent wavefunction of molecules with tens of atoms. AIMS data can be directly compared to the results of ultrafast time-resolved photoelectron spectroscopy data. This allows both the reinterpretation of the experiment and the validation of the simulations. The applicability of time dependent density function theory (TDDFT) to the study of photochemistry is analyzed. TDDFT is found to behave pathologically and alternative approaches are considered. A method to optimize conical intersection points with the accurate multi-state complete active space self consistent field method is also presented. Finally, the possibility of using video game consoles as low cost, high performance tools for the study of photochemistry and scientific computing in general. These various methods are applied to study the photochemistry of two isomerizable molecules: 1,3-butadiene and stilbene. |
