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The potential energy surface of the Fe dimer was investigated on the basis of density functional theory in the generalized gradient approximation (GGA). Results showed that explicit consideration of on-site Coulomb repulsion within the CGAU method has a strong effect on the potential energy surface of the Fe dimmer.

To shed light on the metal 3d electronic structure of manganese phthalocyanine, so far controversial, we performed photoelectron measurements both in the gas phase and as thin film. With the purpose of explaining the experimental results,three different electronic configurations close in energy to one another were studied by means of density functional theory. The comparison between the calculated valence band density of states and the measured spectra revealed that in the gas phase the molecules exhibit a mixed electronic configuration, while in the thin film, manganese phthalocyanine finds itself in the theoretically computed ground state, namely, the b1(2g)e3(g)a1(1g)b0(1g) electronic configuration.

The potential energy surface of the Fe dimer is investigated on the basis of density functional theory in the generalized gradient approximation (GGA). Electron correlation effects are taken into account explicitly within the GGA+U approach. We find a value of 2.20 eV for the Coulomb repulsion parameter U to describe the Fe dimer best, yielding a 9 Sigma(g)- ground state with an interatomic separation of 2.143 A. Agreement of the associated vibrational frequency, binding energy, ionization potential, and electron affinity with experimental data as well as corresponding results calculated within a high-level ab initio approach is improved significantly compared to conventional GGA. The effect of U on calculated geometric and magnetic properties of larger Fe clusters is discussed.