DFT and MP2 calculations of the static dipole hyperpolarizabilities of DAAD Quadrupolar Molecules

We report a theoretical study of the electron correlation, basis sets and substituent effects on the average of the dipole polarizability and second hyperpolarizability, <α> and <γ>, respectively, of a pair of DAAD quadrupolar isomers. The geometric optimization calculations were carried out at the HF, MP2 and DFT (B3LYP and BHHLYP) levels of theory using different basis sets. The results show that the electron correlation effects for the dipole polarizability <alpha> are consistent between the MP2 and DFT levels, whereas for the second hyperpolarizability <γ> the DFT performance shown significant differences with respect to the corresponding MP2 results. This behavior does not change with the variation of the employed basis sets.

Regarding to the substituent effects, the results show that electron donor groups in conjunction with extended basis sets increase the values of <alpha> and <γ> at all levels of theory. In particular, -N(CH₃)₂ and -OCH₃ groups are the substituents that lead to the highest values for these properties. We have also found that there exists a geometry dependency associated to the type of isomer on the <gamma> values.