The ab initio multiple spawning (AIMS) method is a time-dependent formulation of quantum chemistry, whereby the nuclear dynamics and electronic structure problems are solved simultaneously. Quantum mechanical effects in the nuclear dynamics are included, especially the nonadiabatic effects which are crucial in modeling dynamics on multiple electronic states. The AIMS method makes it possible to describe photochemistry from first principles molecular dynamics, with no empirical parameters. We describe the method and present the application to two molecules of interest in organic photochemistrysethylene and cyclobutene. We show that the photodynamics of ethylene involves both covalent and ionic electronic excited states and the return to the ground state proceeds through a pyramidalized geometry. For the photoinduced ring opening of cyclobutene, we show that the disrotatory motion predicted by the Woodward-Hoffmann rules is established within the first 50 fs after optical excitation.
/npsi/ctrl?action=rtdoc&an=12338313&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=12338313&lang=fr READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
The photochemistry of stilbene is investigated using ab initio quantum chemistry with complete active space self-consistent field (CASSCF) and multireference perturbation theory (CASPT2) methods. We characterize photoisomerization pathways from both the cis and trans isomers, including a minimal energy conical intersection. Similarities to photoisomerization in ethylene are found and emphasized. In contrast to traditional one-dimensional models of stilbene photoisomerization, torsion and pyramidalization are required to reach the minimal energy conical intersection which is expected to dominate in quenching to the ground electronic state. This intersection is characterized as an interaction between charge transfer and covalent states. The present results suggest that the qualitative features of the photoisomerization dynamics elucidated for ethylene can also be expected to apply to stilbene, and call for reconsideration and refinement of the photoisomerization mechanism in stilbene.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.