A linear combination of Gaussian-type orbitals (LCGTO) Xα study of ferrocene: The metal-to-ring distance and ionization potentials

The metal-to-ring distance of ferrocene, Fe(C5H5)2, has been optimized using the LCGTO-Xα method. The resulting distance is 0.047 Å shorter than the experimental value of 1.65 Å. The corresponding symmetric stretching frequency of 331 cm−1 shows good agreement with experiment (303 cm−1). The two lowest (Fe 3d derived) ionization potentials are calculated almost degenerate but in reverse order compared to experiment (2A′1 below 2E2). The errors of all these results are discussed in the light of known inadequacies of the local density approximation.