Hello everybody !
I am working on a medium size organic molecule (around 40 atoms) and I try to check the presence of a conical intersection between S1 and S0. I used DFT and TD-DFT to compute the PES of S0 and S1 in my molecule along different modes and motions but for now no conical intersection was identified.
Do you think it would be a possible and interesting approach to use TD-DFT/MD simulation to start from the S1 optimized geometry and apply temperature to check the evolution of the geometry in the S1 state of the molecule in time ? Will it go back to the S0 optimized geometry in the case of an easy accessible conical intersection ?
Thank you for any help you may provide and for your interesting comments about it.
Trying to find a CI through TDDFT using the ground state and its excited state is not a good approach, since the TDDFT isn't able to describe such CI properly (there are even dimensionality errors in the CI space!).
The best way I can remember is to use T1 as the reference state and calculate S0 and S1 as excited states of T1 using splin flip approaches. I don't know which softwares you are using, but ORCA Quantum Chemistry provides an easy way to do it, even though it is possible in most codes.
Depending on the size of your system and the timescales involved, consider employing enhanced sampling techniques like replica exchange or metadynamics to enhance conformational sampling. It's always a good idea to validate your findings using other methods. If possible, consider using other electronic structure methods or non-adiabatic molecular dynamics simulations.
Yes, using Time-Dependent Density Functional Theory (TD-DFT) combined with Molecular Dynamics (MD) simulations can be a viable approach to find conical intersections.
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