Effect of the relative orientation of the CN moieties on the static electric (hyper)polarizability of (CN)2

Abstract

We report static electric (hyper)polarizability values of the three linear isomers of (CN)2. Large, flexible basis sets have been especially designed for all three molecules and the electric properties have been obtained from finite-field Møller–Plesset perturbation theory and coupled cluster calculations. All three molecules are characterized by large polarizability anisotropies. Self-consistent field calculations of near-Hartree–Fock quality yield the following mean polarizabilities: for CN–NC, 32.42 for NC–CN and 33.46 for CN–CN. For the second hyperpolarizability we obtain for CN–NC, 3090 for NC–CN and 3748 for CN–CN. Thus, electric (hyper)polarizability increases in the order NC–CN<CN–CN<CN–NC at the Hartree–Fock level of theory. Electron correlation does not modify this order. Our final estimates suggest that the relative orientation of the two CN moieties in CN–NC produces the most pronounced nonlinear polarizability effect.