Single (C–C) and triple (CC) bond-length dependence of the static electric polarizability and hyperpolarizability of H–CC–CC–H

Abstract

We report an ab initio study of the static electric (hyper)polarizability of diacetylene and its dependence on the single (C–C) and triple (CC) bond length. At the CCSD(T) level of theory we find for the mean dipole polarizability and its derivatives α ̄ =49.10 e 2 a 0 2 E h −1,( ∂ α ̄ / ∂R C− C ) e=−4.41 and ( ∂ α ̄ / ∂R C C ) e=34.57 e 2 a 0 E h −1 . For the anisotropy Δα=54.45 e 2 a 0 2 E h −1 , (∂Δ α/∂ R C–C) e =−20.42 and ( ∂Δα/ ∂R C C ) e=64.56 e 2 a 0 E h −1 . The dependence of the mean hyperpolarizability on R C–C and R CC around the equilibrium is quite distinct. Varying the single bond by Δ R/ a 0 around the equilibrium entails changes of [ γ ̄ (R C– C )− γ ̄ (R e)]/ e 4 a 0 4 E h −3=−3643 ΔR−230 ΔR 2−184 ΔR 3+453 ΔR 4 The mean second hyperpolarizability increases strongly with R C≡C around the equilibrium [ γ ̄ (R C C )− γ ̄ (R e)]/ e 4 a 0 4 E h −3=22 259 ΔR+11 293 ΔR 2+2384 ΔR 3+6445 ΔR 4