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

TL;DR

This study uses density functional theory to analyze how the electronic and vibrational polarities of NaF nanocrystals evolve from diatomic molecules to bulk crystals, revealing size-dependent properties and structural stability.

Contribution

It provides new insights into the size-dependent evolution of polarizability and stability of NaF clusters, including the stability of cubic structures over distorted ones.

Findings

Vibrational to electronic polarizability ratio increases with cluster size.

Na_14F_13 exhibits greatly enhanced electronic polarizability.

Cubic O_h structure is stable compared to distorted structures.

Abstract

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 Na_14F_13 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 O_h cubic structure to be stable relative to the polar distorted structures such as C_3v.