Basis set superposition error in calculations of nonadditive effects in Li(NH3)n and Li(NH3)n+ (n=1–4) clusters

The effect of the basis set superposition error is investigated at both SCF and correlated levels, using the pairwise additive function counterpoise (PAFC), the site-site function counterpoise (SSFC), and the White and Davidson method, for [Li(NH3)n]q+ (n=1–4; q=0, 1) clusters. The PAFC method gives results surprisingly close to the ones obtained with the SSFC approximation. The SSFC, and White and Davidson methods give the possibility of a meaningful decomposition of the total interaction energy of the many-body cluster into its n-body components. The obtained results show that the White–Davidson method is more correct, and always gives the BSSE corrections with the right sign. Moreover it is presented that the effect of the geometry distortions of the interacting particles is so small, that it can be omitted.