A comparison between multireference CI and effective medium theories for diatomic FeN

Summary Internally contracted multireferece CI calculations have been performed for the diatomic molecules FeN, CrN and CrO. For the latter two molecules the calculated dissociation energies are 3.18 eV (3.9±0.2 eV) and 4.09 eV (4.5±0.1 eV) respectively, where the corresponding experimental results are given in parentheses. It is argued that the correct value for CrN must lie in the lower end of the range given by experiment or perhaps slightly below. The best calculated result for FeN, for which no experimental result exists, is 1.69 eV. This value can be compared to an older CI value of 0.9 eV and a recent result of 5.25 eV obtained by an effective medium approach. Based on the results for all the three molecules treated here the correct dissociation energy of FeN can be estimated to be about 2.1 eV. The relevance of the present results for modelling chemical reactions in the regions around on-top positions of transition metal surfaces is discussed.