I'm finishing my Ph.D. in Inorganic Chemistry and having a debate with my supervisor. The work in question have two organometallic compounds A and B. The structures are based on X-Ray Diffraction, so I already have a good molecular frame and just need to optimize the hydrogens. For that I'm using PBEh-3c that usually work well for organometallics. In the next steps, using the now pre-optimized structure, I have changed the level of theory for each task, selecting the (supposedly) best level for each, based on benchmarks:
- Broken-symmetry (magnetic coupling): TPSS/Def2-TZVP
- Bond Orders and spin distribution: SCS-MP2/Def2-TZVP
- Energy Decomposition: DLPNO-CCSD(T)/Def2-TZVP
- TDDFT: wB2PLYP/Def2-TZVP
My Supervisor is not comfortable with the mix of levels of theory, but I believe that it is OK if I'm sure that I have the correct ground-state geometry and I'm not comparing the same property for A and B with different methods (for example TDDFT using PBE for compound A and wB2PLYP for compound B).
So, the question is: is it OK to change the level of theory of my calculations to select the best setup for the property I'm trying to calculate if I know that I have a good ground-state geometry and that my calculation is not displacing the geometry?