Quantitative Structure−Property Relationships for Longitudinal, Transverse, and Molecular Static Polarizabilities in Polyynes

The present work reports for the first time quantitative structure−property relationships, derived at the benchmark CCSD(T)/cc-PVTZ level of theory that estimate the static longitudinal, transverse, and molecular polarizability in polyynes (C2n H2), as a function of their length (L). In the case of independent electron models, regardless of the form of the nuclei potential that the electrons experience, the polarizability increases strongly with system size, scaling as L 4. In contrast, the static longitudinal polarizability in polyynes have a considerably weaker length-dependence (L 1.64). This is shown to predominantly arise from electron−electron repulsion rather than electron correlation by a systematic study of the polarizability length dependence in several simple quantum mechanical systems (e.g., particle-in-box, simple harmonic oscillator) and other molecular systems (e.g., H2, H2 +, polyynes). Decrease of the electron−electron repulsion term is suggested to be the key factor in enhancing nonlinear polarizability characteristics of linear oligomeric and polymeric materials.