Hi,
I have a question regarding transition state (TS) calculations using the SF-TDDFT method in Q-Chem. I understand that analytic Hessians are not available for SF-TDDFT.
In my current workflow, I have:
- Optimized all reaction intermediates using SF-TDDFT (analytic gradients available), and
- Optimized the transition state at the DFT level, followed by a frequency calculation.
My question is: Is it acceptable to perform only a single-point SF-TDDFT calculation on the DFT-optimized TS geometry and use these energies together with the SF-TDDFT–optimized intermediates to construct the potential energy surface (PES)?
In other words, can a PES be considered reliable if the intermediates are optimized at the SF-TDDFT level, while the TS geometry comes from DFT and is characterized at the SF-TDDFT level only via single-point calculations?
Any guidance or best-practice recommendations would be greatly appreciated.