Energy interaction, closed-subshell atoms

It indicates that, the physical sense of the 2-body SCF energy in trimers is the same as the SCF interaction energy in dimers it is predominantly the exchange interactions which are repulsive for two interacting atoms with closed subshells. The attractive contributions from the electrostatic and induction energies are less than the repulsive exchange contribution. This is the reason that CF(A3) is positive for the alkaline trimers in all calculated distance regions [22]. 

In every case a careful analysis of the configurations that are included in this large Cl scheme is carried out trying to determine how their role during the process is to be understood. Such configurations represent very often a polarization of the d-subshell, which in many cases is closed or nearly closed, so that its relaxation substantially lowers the interaction energy between a transition metal atom and a small closed-shell molecule... 

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