Evolution of Electronic and Vibrational Polarity of NaF Nanocrystals from Diatomic to Bulk: A Density Functional Study

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Density functional theory (DFT) is used to study vibrations, electrical dipole moments, and polarizabilities of NaF clusters. Because of prior experimental and theoretical studies, this is a good model system for tracking the evolution of the properties from diatomic molecule to bulk crystal. The ratio of vibrational to electronic contributions to the polarizability increases dramatically with size N in the closed shell clusters (NaF)ₙ. The open shell system Na₁4F₁3 has a greatly enhanced electronic polarizability. Contrary to previous studies on this system which treated only the outer electron by quantum mechanics, we find the Oₕ cubic structure to be stable relative to the polar distorted structures such as C₃v.