Fast Screening of Minimum Energy Crossing Points with Semiempirical Tight-Binding Methods

The investigation of photochemical processes is a highly
active
field in computational chemistry. One research direction is the automated
exploration and identification of minimum energy conical intersection
(MECI) geometries. However, due to the immense technical effort required
to calculate nonadiabatic potential energy landscapes, the routine
application of such computational protocols is severely limited. In
this study, we will discuss the prospect of combining adiabatic potential
energy surfaces from semiempirical quantum mechanical calculations
with specialized confinement potential and metadynamics simulations
to identify S0/T1 minimum energy crossing point
(MECP) geometries. It is shown that MECPs calculated at the GFN2-xTB
level can provide suitable approximations to high-level S0/S1ab initio conical intersection geometries
at a fraction of the computational cost. Reference MECIs of benzene
are studied to illustrate the basic concept. An example application
of the presented protocol is demonstrated for a set of photoswitch
molecules.