Observations on Computing High Spin Fe systems

• SCF at ROHF level, medium to large basis set, can be unstable/unpredictable:
  1. Quintets: GAMESS-US optimal package
  2. Quartets: Gaussian03 optimal package
  3. Sextets: GAMESS-UK optimal package
• SCF at ROHF level, ΔE Quartet/Sextet wrong.
• SCF at B3LYP DFT level, unstable/unconvergable. ΔE Quartet/Sextet wrong
• SCF at KMLYP DFT level, unstable/unconvergable. ΔE Quartet/Sextet correct
• Vibrational Frequencies (Transition states)
  1. Numerical frequencies only (G03, GAMESS-US) due to lack of code for f-functions on Fe
  2. Numerical frequencies require SCF convergence to 10^-6 or better
  3. Analytic frequencies: GAMESS-UK, 2006 version only. No advanced ROHF SCF converger.