Basis set and method dependence in atoms in molecules calculations.

The influence of various basis sets used in HF and DFT/B3LYP calculations to the values of atoms in molecules (AIM) parameters derived from the electron density distibution for weak hydrogen-bonded systems is investigated. Using three model complexes, F(3)CH...NH(3), F(3)CH...NCH, and FCCH...NH(3), we show that values of the most important AIM parameters calculated in the bond critical point of the H...N hydrogen bond are almost independent of both the method and the basis set. Only the smallest Dunning-type cc-pVDZ or aug-cc-pVDZ basis sets may lead to poor results, whereas even medium-sized Pople-type basis sets can give reasonable results converting to those obtained from the use of large Dunning-type basis sets.