Systematic study of the basis set superposition error in core-electron correlation effects.

In a recent paper, Xu et al. [J. Phys. Chem. A 2012, 116, 11668] emphasized the importance of core-electron correlation effects to describe the Si2H6BH3 complex and related systems properly. Unexpected large energy differences between a frozen core and all electron treatment were observed. In the present study, it will be shown that these energy differences are an artifact of an insufficient choice of basis set and can be attributed to an intramolecular basis set superposition error (BSSE). Although the general problem is known, systematic studies on the effect are scarce. Therefore, the BSSE in related systems is investigated. This study shows that the problem of BSSE for core-electron correlation is quite common if inadequate basis sets are applied and that it amounts to 2 kcal mol(-1) on average in binding energies for the given test set (with a maximum of 5.8 kcal mol(-1)).