Differential correlation energy calculations

The MP2 calculations were intended to provide an estimate of the differential correlation energy associated with various valence-state configurations. Accordingly, the ls-2p(Co) and ls(N) cores were not active in the MP2 calculations. Extension of the Co core to include the 3s/3p shell was found to yield results similar to those based on the ls-2p core, and some of the results reported below were obtained at this level. 

The zero differential overlap approximation can be applied in the localized representation. This was demonstrated by calculating for C H, CioTfio and C14//14, respectively the total energy corrections and the pair correlation energies through second and third order in different approximations. When the strongly local contributions were only... 

Table I contrasts relative energies of the relevant atomic states with corresponding experimental values [2]. Notice the good agreement between the calculated and experimental Pg<- Pu energy splitting of the B atom. On the contrary, the calculated separations Dg<- Dg and Fg - Dg of the Sc atom are not in satisfactory agreement with the experimental results, the largest discrepancy being 0.137 eV ( Fg<- Dg), due to differential correlation effects [25].

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