Erroneous behaviour of the widely used MP2(full)/aug-cc-pVXZ (X = D,T) level of theory for evaluating the BSSE in ion-π complexes

The calculations of several ion-π complexes have been optimized using the MP2 method and several double-ζ and triple-ζ basis sets. The BSSE (basis set superposition error) counterpoise correction on the ion-π complexes was computed for Pople's and Dunning's basis sets using both frozen core and full core MP2 methods. An anomalous behaviour of the widely used MP2(full)/aug-cc-pVXZ (X = D,T) level of theory was observed, specially for sodium complexes.