Interpretations of the Basis-set Superposition Error

Although it is possible to use Eq. (20) directly, without any explicit consideration of a quantity called BSSE, it is customary to start from Eq. (19) and to consider the correction 5 that would remove the BSSE in (19), viz. 

Johansson et al were the first to conclude that the counterpoise procedure overestimates the basis-set superposition error. They proposed to scale the correction by a factor reflecting the reduced number of ghost virtual orbitals available to a monomer in the dimer situation and obtained good agreement with larger basis sets for their STO-3G SCF calculations on hydrogen-bonded systems. Their idea has had few followers and little. Nevertheless, their conclusion that the BSSE is overestimated 

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