A consistent description of the iron dimer spectrum with a correlated single-determinant wave function

We study the iron dimer by using an accurate ansatz for quantum chemical calculations based on a simple variational wave function, defined by a single geminal expanded in molecular orbitals and combined with a real space correlation factor. By means of this approach we predict that, contrary to previous expectations, the neutral ground state is (7)Delta while the ground state of the anion is (8)Sigma(-)(g), hence explaining in a simple way a long standing controversy in the interpretation of the experiments. Moreover, we characterize consistently the states seen in the photoemission spectroscopy by Leopold and Lineberger [D. G. Leopold, W. C. Lineberger, J. Chem. Phys. 85 (1) (1986) 51]. It is shown that the non-dynamical correlations included in the geminal expansion are relevant to correctly reproduce the energy ordering of the low-lying spin states. (C) 2009 Elsevier B. V. All rights reserved.