Static hyperpolarizabilities and polarizabilities of linear polyynes

The dipole polarizability(α) and second dipole hyperpolarizability(γ) tensors are calculated, by finite-field methods, for the ground states of butadiyne, hexatriyne, and octatetrayne. The effects of varying one-particle basis sets and molecular geometry, and the effects of including electron correlation at the fourth-order many-body perturbation theory level, are examined for butadiyne. The hyperpolarizabilities are more sensitive to geometry changes than to electron correlation. Coupled self-consistent-field calculations on hexatriyne and octatetrayne indicate that the longitudinal components αzz and γzzzz, grow as n1.5 and n3.0, respectively, and that the mean values ᾱ and γ̄ grow as n1.2 and n2, respectively, as the chain length increases in the C2nH2 series.