posted on 2013-02-12, 00:00authored byToshifumi Mori, Todd. J. Martínez
Conical intersections (CIs) play a fundamental role in
photoreactions.
Although it is widely known that CIs are not isolated points but rather
multidimensional seams, there is a dearth of techniques to explore
and characterize these seams beyond the immediate vicinity of minimum
energy points within the intersection space (minimum energy conical
intersections or MECIs). Here, we develop a method that connects these
MECIs by minimal energy paths within the space of geometries that
maintain the electronic degeneracy (the “seam space”)
in order to obtain a more general picture of a CI seam. This method,
the seam space nudged elastic band (SS-NEB) method, combines the nudged
elastic band method with gradient projected MECI optimization. It
provides a very efficient way of finding minimum energy seam paths
in the conical intersection seam. The method is demonstrated by application
to two molecules: ethylene and the green fluorescent protein (GFP)
chromophore. The results show that previously known MECIs for these
molecules are connected within a single seam, adding further support
to previous conjectures that all MECIs are topologically connected
in the seam space. Analysis of the nonadiabatic dynamics further suggests
that a broad range of seam geometries, not only the vicinity of MECIs,
is involved in the nonadiabatic transition events. The current method
provides a tool to characterize CI seams in different environments
and to explore the importance of the seam in the dynamics.