| Abstract
| - We investigated the performance of the B3LYP density functional in combination with ab initio effectivecore potentials (ECPs) that are derived from either Hartree−Fock or Dirac−Fock calculations. Thetransferability of ab initio ECPs is assessed on the basis of comparison with all-electron density functionalcalculations. For iron(II) porphyrin in particular, our assessment focused on the relative energetic orderingof five low-lying spin states, 1A1G, 3A1G, 3B2G, 5A2G, and 5B1G, and their properties, including optimizedstructures, charge distribution, spin density, and vibrational frequencies. Our results show that core electroncorrelation and core−valence electron correlation do not have significant effects on the relative energeticsof the spin states of iron porphyrin. Our calculations suggest that effects of replacing the core electronswith ECPs are less significant than the choice of basis functions. We conclude that ab initio ECPs such asLANL2, RCEP, and MEFIT-R may be combined with the B3LYP density functional theory to provideconsistent and accurate results.
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