Interaction-induced electric properties and cooperative effects in model systems.

A detailed analysis of the interaction-induced linear and non-linear axial static electric dipole properties and the interaction energy of the model HCHO(HF)(n) (n = 1, 2) complexes is carried out using the HF SCF, MP2, CCSD and CCSD(T) levels of approximation combined with a wide range of basis sets, namely the correlation-consistent basis sets of Dunning and co-workers, the polarization-consistent basis sets of Jensen, and the recently reported polarized LPol sets. The results of this study show that even the smallest among the LPol sets, the LPol-ds and LPol-dl sets, yield interaction induced axial static electric dipole properties of an accuracy comparable to that obtained with the aug-cc-pVQZ basis set. Using the LPol-ds, the LPol-dl, and the LPol-fl sets we have estimated the induced electric properties and the interaction energy of the HCHO(HF)(n) (n = 1-9) complexes, the cooperative effects in these systems, and the two-body effects. The many-body analysis shows that the two-body contributions to the induced first hyperpolarizability are not sufficient to correctly reproduce the general tendency for the changes in the property with the elongation of the polymer chain, since already for the n = 4 complex the more-than-two-body terms become dominant.