Static Polarizabilities (α) and Second Hyperpolarizabilities (γ) of One-Dimensional Hydrogen-Bonded Formamides

We investigate the chain length dependences of static polarizabilities (α) and second hyperpolarizabilities (γ) for one-dimensional hydrogen (H)-bonded chains composed of formamide from the viewpoint of cooperative effect of H-bonds. The α and γ values are calculated by the finite-field approach using the Hartree-Fock (HF), Moller-Presset perturbation theory (MP) and density functional theory (DFT) methods in order to clarify the electron correlation effects on the α and γ values of the H-bonded systems. The increase ratio of γ values per monomer for the increase of the number of monomers is found to be significantly enhanced compared to that of α values per monomer. This feature suggests the strong cooperative effects on γ originating in the interaction between the H-bonds and π-electrons of the monomers in the high-lying excited states mainly contributing to γ.